Fix List memory issue in transformColumnDefinition

 Fix List memory issue in transformColumnDefinition
 
 When calling generateSerialExtraStmts(), we would pass in the
 constraint->options.  In some cases, generateSerialExtraStmts() would
 modify the referenced List to remove elements from it, but doing so is
 invalid without assigning the list back to all variables that point to it.
 In the particular reported problem case, the List became empty, in which
 cases it became NIL, but the passed in constraint->options didn't get to
 find out about that and was left pointing to free'd memory.
 
 To fix this, just perform a list_copy() inside generateSerialExtraStmts().
 We could just do a list_copy() just before we perform the delete from the
 list, however, that seems less robust.  Let's make sure the generated
 CreateSeqStmt gets a completely different copy of the list to be safe.
 
 Bug: #17879
 Reported-by: Fei Changhong
 Diagnosed-by: Fei Changhong
 Discussion: https://postgr.es/m/17879-b7dfb5debee58ff5@postgresql.org
 Backpatch-through: 11, all supported versions