We'll be fixing soon shift-reduce conflicts introduced in the new
10.3 syntax (see MDEV-15818 for details) by defining precedence for
a number of tokens (e.g. TIMESTAMP, TRANSACTION_SYM, TEXT_STRING)
and adding "%prec" directives.

Before doing this, it's better to have the existing precedences set properly,
for easier readability and maintainability.

Details:
- Changing precedence of NOT to its proper position (between AND and IS).
  It was wrong. It worked fine only because the relevant grammar reside
  in different separate rules (expr and predicate).

- Moving NOT2_SYM and BINARY to the same line with NEG and ~
  It worked fine because operators !, BINARY, ~ do not conflict
  to each other.

- Fixing associativity of NOT_SYM, NOT2_SYM, BINARY, COLLATE_SYM
  from "right" to "left". They are not dyadic (operate on a single expression
  only). So "%left" or "%right" is needed only to set precedence,
  while associativity does not matter.
  Note, it would be better to use "%precedence" for these tokens
  instead of "%left" though, but we use an old version of Bison on windows,
  which may not support %precedence yet.

This patch does not change behavior. The generated sql_yacc.cc and
sql_yacc_ora.cc are exactly the same before and after this change.