gh-73588: Fix generation of the default name of tkinter.Checkbutton. (GH-97547)

Previously, checkbuttons in different parent widgets could have the same
short name and share the same state if arguments "name" and "variable" are
not specified. Now they are globally unique.
(cherry picked from commit adbed2d542a815b8175db965742211856b19b52f)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>