- new test case for pre-initialization of sys.warnoptions and sys._xoptions
- restored ability to call these APIs prior to Py_Initialize
- updated the docs for the affected APIs to make it clear they can be
  called before Py_Initialize
- also enhanced the existing embedding test cases
  to check for expected settings in the sys module

Skip the test failing randomly because of known race condition.

Skip the test to fix macOS buildbots until a decision is made on the
proper fix for the race condition.

When PyGILState_Ensure() is called in a non-Python thread before
PyEval_InitThreads(), only call PyEval_InitThreads() after calling
PyThreadState_New() to fix a crash.

Add an unit test in test_embed.

Some parts of the C API are only relevant to larger
applications embedding CPython as a runtime engine.

The helpers to test those APIs are already separated
out into Programs/_testembed.c, this update moves
the associated test cases out into their own dedicated
test file.