Introduce Type_handler::make_in_vector() and Item_func_in_fix_comparator_compatible_types()

This task will:

1. Introduce new Type_handler methods:

virtual in_vector *make_in_vector(THD *thd, const Item_func_in *func, uint nargs) const;

virtual bool Item_func_in_fix_comparator_compatible_types(THD *thd, Item_func_in *) const;

2. Remove these data type conditions in Item_func_in::fix_length_and_dec()

• switch (m_comparator.cmp_type())
• if (m_comparator.cmp_type() == STRING_RESULT
• if (m_comparator.cmp_type() == ROW_RESULT)
• if ... m_comparator.cmp_type() != INT_RESULT

and use the new Type_handler methods instead.

3. Split in_datetime (which now covers all temporal data types: DATETIME, DATE, TIME) into an abstract parent class in_temporal and two instantiable classes in_datetime (for DATETIME and DATE) and in_time (for TIME).

After this change the behavior of the code responsible for IN bisection search will be fully handled by Type_handler.

There will some explicit XXX_RESULT conditions be left though, in the code responsible for the cmp_items based IN search. This code will be cleaned-up in a separate patch.