[3.15] gh-155561: Build most _testlimitedcapi files with Py_TARGET_ABI3T (#155570) (#159144)

* gh-155561: Build most _testlimitedcapi files with Py_TARGET_ABI3T (#155570)

The following files are not build with Py_TARGET_ABI3T:

* Modules/_testlimitedcapi.c
* Modules/_testlimitedcapi/heaptype_relative.c
* Modules/_testlimitedcapi/vectorcall_limited.c

(cherry picked from commit 5dfa606af39d1e21d130205ce0efbb7a10e124f7)

* gh-155561: Use multi-phase init for Modules/_testlimitedcapi.c (GH-156052)

Co-authored-by: Victor Stinner <vstinner@python.org>
(cherry picked from commit 112560ee34a70c02baebdc11519d1f77e90ecab8)

---------

Co-authored-by: Petr Viktorin <encukou@gmail.com>