Move set_param_xxx() in sql_prepare.cc to methods in Item_param and Type_handler

Under terms of this task we'll:

• Change a virtual function pointer Item_param::set_param_func to a Type_handler based implementation, by adding a new virtual method Type_handler::Item_param_set_param_func()

• Move static functions set_param_xxx() as methods to Item_param

• Decompose the switch in setup_one_conversion_function() into a new virtual method Type_handler::Item_param_setup_conversion()