Step#1: fixing the return type of strnxfrm() from size_t to this structure:

typedef struct
{
  size_t m_output_length;
  size_t m_source_length_used;
  uint m_warnings;
} my_strnxfrm_ret_t;

This patch also fixes:
  MDEV-33050 Build-in schemas like oracle_schema are accent insensitive
  MDEV-33084 LASTVAL(t1) and LASTVAL(T1) do not work well with lower-case-table-names=0
  MDEV-33085 Tables T1 and t1 do not work well with ENGINE=CSV and lower-case-table-names=0
  MDEV-33086 SHOW OPEN TABLES IN DB1 -- is case insensitive with lower-case-table-names=0
  MDEV-33088 Cannot create triggers in the database `MYSQL`
  MDEV-33103 LOCK TABLE t1 AS t2 -- alias is not case sensitive with lower-case-table-names=0
  MDEV-33109 DROP DATABASE MYSQL -- does not drop SP with lower-case-table-names=0
  MDEV-33110 HANDLER commands are case insensitive with lower-case-table-names=0
  MDEV-33119 User is case insensitive in INFORMATION_SCHEMA.VIEWS
  MDEV-33120 System log table names are case insensitive with lower-cast-table-names=0

- Removing the virtual function strnncoll() from MY_COLLATION_HANDLER

- Adding a wrapper function CHARSET_INFO::streq(), to compare
  two strings for equality. For now it calls strnncoll() internally.
  In the future it will turn into a virtual function.

- Adding new accent sensitive case insensitive collations:
    - utf8mb4_general1400_as_ci
    - utf8mb3_general1400_as_ci
  They implement accent sensitive case insensitive comparison.
  The weight of a character is equal to the code point of its
  upper case variant. These collations use Unicode-14.0.0 casefolding data.

  The result of
     my_charset_utf8mb3_general1400_as_ci.strcoll()
  is very close to the former
     my_charset_utf8mb3_general_ci.strcasecmp()

  There is only a difference in a couple dozen rare characters, because:
    - the switch from "tolower" to "toupper" comparison, to make
      utf8mb3_general1400_as_ci closer to utf8mb3_general_ci
    - the switch from Unicode-3.0.0 to Unicode-14.0.0
  This difference should be tolarable. See the list of affected
  characters in the MDEV description.

  Note, utf8mb4_general1400_as_ci correctly handles non-BMP characters!
  Unlike utf8mb4_general_ci, it does not treat all BMP characters
  as equal.

- Adding classes representing names of the file based database objects:

    Lex_ident_db
    Lex_ident_table
    Lex_ident_trigger

  Their comparison collation depends on the underlying
  file system case sensitivity and on --lower-case-table-names
  and can be either my_charset_bin or my_charset_utf8mb3_general1400_as_ci.

- Adding classes representing names of other database objects,
  whose names have case insensitive comparison style,
  using my_charset_utf8mb3_general1400_as_ci:

  Lex_ident_column
  Lex_ident_sys_var
  Lex_ident_user_var
  Lex_ident_sp_var
  Lex_ident_ps
  Lex_ident_i_s_table
  Lex_ident_window
  Lex_ident_func
  Lex_ident_partition
  Lex_ident_with_element
  Lex_ident_rpl_filter
  Lex_ident_master_info
  Lex_ident_host
  Lex_ident_locale
  Lex_ident_plugin
  Lex_ident_engine
  Lex_ident_server
  Lex_ident_savepoint
  Lex_ident_charset
  engine_option_value::Name

- All the mentioned Lex_ident_xxx classes implement a method streq():

  if (ident1.streq(ident2))
     do_equal();

  This method works as a wrapper for CHARSET_INFO::streq().

- Changing a lot of "LEX_CSTRING name" to "Lex_ident_xxx name"
  in class members and in function/method parameters.

- Replacing all calls like
    system_charset_info->coll->strcasecmp(ident1, ident2)
  to
    ident1.streq(ident2)

- Taking advantage of the c++11 user defined literal operator
  for LEX_CSTRING (see m_strings.h) and Lex_ident_xxx (see lex_ident.h)
  data types. Use example:

  const Lex_ident_column primary_key_name= "PRIMARY"_Lex_ident_column;

  is now a shorter version of:

  const Lex_ident_column primary_key_name=
    Lex_ident_column({STRING_WITH_LEN("PRIMARY")});

This is a non-functional change. It changes the way how case folding data
and weight data (for simple Unicode collations) are stored:

- Removing data types MY_UNICASE_CHARACTER, MY_UNICASE_INFO
- Using data types MY_CASEFOLD_CHARACTER, MY_CASEFOLD_INFO instead.

This patch changes simple Unicode collations in a similar way
how MDEV-30695 previously changed Asian collations.

No new MTR tests are needed. The underlying code is thoroughly
covered by a number of ctype_*_ws.test and ctype_*_casefold.test
files, which were added recently as a preparation
for this change.

Old and new Unicode data layout
-------------------------------

Case folding data is now stored in separate tables
consisting of MY_CASEFOLD_CHARACTER elements with two members:

    typedef struct casefold_info_char_t
    {
      uint32 toupper;
      uint32 tolower;
    } MY_CASEFOLD_CHARACTER;

while weight data (for simple non-UCA collations xxx_general_ci
and xxx_general_mysql500_ci) is stored in separate arrays of
uint16 elements.

Before this change case folding data and simple weight data were
stored together, in tables of the following elements with three members:

    typedef struct unicase_info_char_st
    {
      uint32 toupper;
      uint32 tolower;
      uint32 sort;          /* weights for simple collations */
    } MY_UNICASE_CHARACTER;

This data format was redundant, because weights (the "sort" member) were
needed only for these two simple Unicode collations:
- xxx_general_ci
- xxx_general_mysql500_ci

Adding case folding information for Unicode-14.0.0 using the old
format would waste memory without purpose.

Detailed changes
----------------
- Changing the underlying data types as described above

- Including unidata-dump.c into the sources.
  This program was earlier used to dump UnicodeData.txt
  (e.g. https://www.unicode.org/Public/14.0.0/ucd/UnicodeData.txt)
  into MySQL / MariaDB source files.
  It was originally written in 2002, but has not been distributed yet
  together with MySQL / MariaDB sources.

- Removing the old format Unicode data earlier dumped from UnicodeData.txt
  (versions 3.0.0 and 5.2.0) from ctype-utf8.c.
  Adding Unicode data in the new format into separate header files,
  to maintain the code easier:

    - ctype-unicode300-casefold.h
    - ctype-unicode300-casefold-tr.h
    - ctype-unicode300-general_ci.h
    - ctype-unicode300-general_mysql500_ci.h
    - ctype-unicode520-casefold.h

- Adding a new file ctype-unidata.c as an aggregator for
  the header files listed above.

- Adding a new argument "flag" to MY_COLLATION_HANDLER::strnncollsp_nchars()
  and a flag MY_STRNNCOLLSP_NCHARS_EMULATE_TRIMMED_TRAILING_SPACES.
  The flag defines if strnncollsp_nchars() should emulate trailing spaces
  which were possibly trimmed earlier (e.g. in InnoDB CHAR compression).
  This is important for NOPAD collations.

  For example, with this input:
   - str1= 'a '    (Latin letter a followed by one space)
   - str2= 'a  '   (Latin letter a followed by two spaces)
   - nchars= 3
  if the flag is given, strnncollsp_nchars() will virtually restore
  one trailing space to str1 up to nchars (3) characters and compare two
  strings as equal:
  - str1= 'a  '  (one extra trailing space emulated)
  - str2= 'a  '  (as is)

  If the flag is not given, strnncollsp_nchars() does not add trailing
  virtual spaces, so in case of a NOPAD collation, str1 will be compared
  as less than str2 because it is shorter.

- Field_string::cmp_prefix() now passes the new flag.
  Field_varstring::cmp_prefix() and Field_blob::cmp_prefix() do
  not pass the new flag.

- The branch in cmp_whole_field() in storage/innobase/rem/rem0cmp.cc
  (which handles the CHAR data type) now also passed the new flag.

- Fixing UCA collations to respect the new flag.
  Other collations are possibly also affected, however
  I had no success in making an SQL script demonstrating the problem.
  Other collations will be extended to respect this flags in a separate
  patch later.

- Changing the meaning of the last parameter of Field::cmp_prefix()
  from "number of bytes" (internal length)
  to "number of characters" (user visible length).

  The code calling cmp_prefix() from handler.cc was wrong.
  After this change, the call in handler.cc became correct.

  The code calling cmp_prefix() from key_rec_cmp() in key.cc
  was adjusted according to this change.

- Old strnncollsp_nchar() related tests in unittest/strings/strings-t.c
  now pass the new flag.
  A few new tests also were added, without the flag.

- Fixed possible error in rocksdb/rdb_datadic.cc

MDEV-17502 MDEV-17474 Change Unicode xxx_general_ci and xxx_bin collation implementation to "inline" style

Based on the patch from Daniil Medvedev (a Google Summer of Code task)

- Removing the "diff_if_only_endspace_difference" argument from
  MY_COLLATION_HANDLER::strnncollsp(), my_strnncollsp_simple(),
  as well as in the function template MY_FUNCTION_NAME(strnncollsp)
  in strcoll.ic

- Removing the "diff_if_only_space_different" from ha_compare_text(),
  hp_rec_key_cmp().

- Adding a new function my_strnncollsp_padspace_bin() and reusing
  it instead of duplicate code pieces in my_strnncollsp_8bit_bin(),
  my_strnncollsp_latin1_de(), my_strnncollsp_tis620(),
  my_strnncollsp_utf8_cs().

- Adding more tests for better coverage of the trailing space handling.

- Removing the unused definition of HA_END_SPACE_ARE_EQUAL

between gbk_chinese_ci and big5_chinese_ci.

MDEV-8418 utf16: compare broken bytes as "greater than any non-broken character"