In commit 91599701 (MDEV-25312)
some recovery code for TRUNCATE TABLE was broken
causing a regression in a case where undo log for a RENAME TABLE
operation had been durably written but the tablespace had not been
renamed yet.

row_rename_table_for_mysql(): Add a DEBUG_SYNC point for the
test case, and simplify the logic and trim the error messages.

fil_space_t::rename(): Simplify the operation. Merge the necessary
part of fil_rename_tablespace_check(). If there is no change to
the file name, do nothing.

dict_table_t::rename_tablespace(): Refactored from
dict_table_rename_in_cache().

row_undo_ins_parse_undo_rec(): On rolling back TRX_UNDO_RENAME_TABLE,
invoke dict_table_t::rename_tablespace() even if the table name matches.

os_file_rename_func(): Temporarily relax an assertion that would
fail during the recovery in the test innodb.truncate_crash.