bpo-43760: Add PyThreadState_EnterTracing() (GH-28542)

Add PyThreadState_EnterTracing() and PyThreadState_LeaveTracing()
functions to the limited C API to suspend and resume tracing and
profiling.

Add an unit test on the PyThreadState C API to _testcapi.

Add also internal _PyThreadState_DisableTracing() and
_PyThreadState_ResetTracing().