GH-148726: Forward-port generational GC. (GH-148746)

The replaces the incremental GC with a forward port (from 3.13) of the generational GC.

Co-Authored-By: Neil Schemenauer <nas@arctrix.com>
Co-Authored-By: Zanie Blue <contact@zanie.dev>
Co-Authored-By: Sergey Miryanov <sergey.miryanov@gmail.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>