gh-103092: Isolate _tkinter (WIP)

[erlend-aasland]

TODO

• There's no way to pass state to PyOS_InputHooks. Introduce a new hook with context pointer? Just opt out of multi-phase init / module state for _tkinter? Or just protect these with per-interpreter locks.

• Handle the three Tcl mutexes

• Issue: Isolate Stdlib Extension Modules #103092

[arhadthedev]

There's no way to pass state to PyOS_InputHooks. Introduce a new hook with context pointer?

We can add two private API functions (a name and arguments are up to discussion):

• int _PyOS_suscribesig(int i, void(*)(int, void *) h, void *harg);
• void _PyOS_unsuscribesig(int subscription);

and reimplement PyOS_setsig as a wrapper to avoid conflicts.

By the way, are the signals are process-wide or pthread-wide? If the former, is there a global CPython structure common for all (sub)interpreters?