Part I. Grammar preparation.

* Replace the existent type tag <symbol> with <keyword> for a better
  readability.

* Add the new type tag <keyword> to currently untyped terminal and
  non-terminal symbols.

Part II. Create a simple compile-time program for transforming
         sql_yacc.yy into a .h file that contains an array of
	 reserved and non-reserved words.

* Find %token declarations with the <keyword> type tag by a regexp.

* Separate %type declarations are ignored for the simplicity.

Part III. Introduce a new system view: INFORMATION_SCHEMA.keywords.

* Hardcode the statical list of keywords and reserved words into a view
  on top of a long JSON_TABLE(...) expression.

* Use a trick in the .test file to trace changes in keywords: notify the
  developer to update the target I_S version in the mysqld binary where
  necessary -- this will force DD to refresh I_S view declarations on
  the next run.

Change-Id: Ib40e7f743f4deb069df0a0bbc00c39e4460f7c33