gh-116417: Move limited C API long.c tests to _testlimitedcapi (#117001)

* Split long.c tests of _testcapi into two parts: limited C API tests
  in _testlimitedcapi and non-limited C API tests in _testcapi.
* Move testcapi_long.h from Modules/_testcapi/ to
  Modules/_testlimitedcapi/.
* Add MODULE__TESTLIMITEDCAPI_DEPS to Makefile.pre.in.