Move Item_func_like out of Item_bool_func2

Item_func_like is erroneously inherited from Item_bool_func2.
Unlike the other Item_bool_func2, Item_func_like:

• does not need Arg_comparator
• does not need abort_on_null, as we don't support LIKE for rows: (x1,y1,z1) LIKE (x2,y2,z2)

Wrong inheritance needs excessive casts and functype() calls and potentially more buggy.

See MDEV-8222 as an example of a bug introduced because of this wrong inheritance.

Derive Item_func_like directly from Item_bool_func.

Another option would be to move Arg_comparator from Item_bool_func2 to Item_bool_rowready_func2.