When processing statements with hint comments (/*+...*/), the
digest calculation was skipped for hint expressions, so the same
statement had identical digests with and without hints.
Also, the normalized query text missed hint expressions
in the performance_schema.events_statements_history table.

The fix updates several parts of the server:

1. The gen_lex_token.cc token information file generator:
some tricks to add hint parser internals(*) to the global token
list (lex_token_array) have been introduced.

*) Hint parser internals:
 a. Hint keywords: their integer token values may interfere with
    token values of the main SQL parser, so the TOK_HINT_ADJUST()
    adjustment macro has been introduced to resolve ambiguities.
 b. Tokens for "/*+" and "*/" hint comment delimiters to represent in
    the normalized query text.
 c. The TOK_IDENT_AT token to distinguish unqualified identifiers
    from table names in the table@query_block_name expression.
    Such a special token is necessary to generate normalized
    query texts without a space character between the
    table name and the "@" sign:

      "`table` @`qb_name`" is wrong,
      "`table`@`qb_name`"  is correct.

2. The sql_digest.cc digest calculator and query text normalizer:
the support for the TOK_IDENT_AT token has been added to not output
a space between a table name and a "@query_block_name" suffix.

3. The main lexer (sql_lex.{h,cc}):
the Lex_input_stream::skip_digest flag has been introduced to
append tokens to a digest buffer in correct order: add a
hintable SQL keyword (SELECT, INSERT, UPDATE...) first, then add
a hint expression (/*+ ... */).

4. The hint parser (sql_lex_hints.{h,cc}):
the Hint_scanner::add_hint_token_digest() function has been
added to translate hint parser tokens into main parser-compatible
ones and to add them into a digest buffer.

5. Minor code cleanups:
lex.h and sql_hints.yy: unused token declarations have been removed.