parser cleanup: don't store field properties in LEX, use Create_field directly

length/dec/charset are still in LEX, because they're also used
for CAST and dynamic columns.

also
1. fix "MDEV-7041 COLLATION(CAST('a' AS CHAR BINARY)) returns a wrong result"
2. allow BINARY modifier in stored function RETURN clause
3. allow "COLLATION without CHARSET" in SP/SF (parameters, RETURN, DECLARE)
4. print correct variable name in error messages for stored routine parameters
cleanup: sort and reorder %union elements in sql_yacc.yy
cleanup: comments referring to non-extistent Item classes