MDEV-15703: Crash in EXECUTE IMMEDIATE 'CREATE OR REPLACE TABLE t1 (a INT DEFAULT ?)' USING DEFAULT, UBSAN runtime error: member call on null pointer of type 'struct TABLE_LIST' in Item_param::save_in_field

This is the prerequisite patch to refactor the method
  Item_default_value::fix_fields.
The former implementation of this method was extracted and placed
into the standalone function make_default_field() and the method
Item_default_value::tie_field(). The motivation for this modification
is upcoming changes for core implementation of the task MDEV-15703
since these functions will be used from several places within
the source code.