bpo-43268: Replace _PyThreadState_GET() with _PyInterpreterState_GET() (GH-24576)

Replace _PyThreadState_GET() with _PyInterpreterState_GET() in
functions which only need the current interpreter, but don't need the
current Python thread state.

Replace also _PyThreadState_UncheckedGet() with _PyThreadState_GET()
in faulthandler.c, since _PyThreadState_UncheckedGet() is just an
alias to _PyThreadState_GET() in practice.