gh-116417: Add _testlimitedcapi C extension (#116419)

Add a new C extension "_testlimitedcapi" which is only built with the
limited C API.

Move heaptype_relative.c and vectorcall_limited.c from
Modules/_testcapi/ to Modules/_testlimitedcapi/.

* configure: add _testlimitedcapi test extension.
* Update generate_stdlib_module_names.py.
* Update make check-c-globals.

Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>