Fixing ROUND(date,0), TRUNCATE(date,x), FLOOR(date), CEILING(date)
to return the `int(8) unsigned` data type.

Details:
1. Cleanup: moving virtual implementations
   - Type_handler_temporal_result::Item_func_int_val_fix_length_and_dec()
   - Type_handler_temporal_result::Item_func_round_fix_length_and_dec()
   to Type_handler_date_common. Other temporal data type handlers
   override these methods anyway. So they were only DATE specific.
   This change makes the code clearer.
2. Backporting DTCollation_numeric from 10.5, to reuse the code easier.
3. Adding the `preferred_attrs` argument to Item_func_round::fix_arg_int(). Now
   Type_handler_xxx::Item_func_round_val_fix_length_and_dec() work as follows:
   - The INT-alike and YEAR handlers copy preferred_attrs from args[0].
   - The DATE handler passes explicit attributes, to get `int(8) unsigned`.
   - The hex hybrid handler passes NULL, so fix_arg_int() calculates attributes.
4. Type_handler_date_common::Item_func_int_val_fix_length_and_dec()
   now sets the type handler and attributes to get `int(8) unsigned`.