In preparation for a per-interpreter GIL, we add PyInterpreterState.ceval.gil, set it to the shared GIL for each interpreter, and use that rather than using _PyRuntime.ceval.gil directly.  Note that _PyRuntime.ceval.gil is still the actual GIL.

Here we are doing no more than adding the value for Py_mod_multiple_interpreters and using it for stdlib modules.  We will start checking for it in gh-104206 (once PyInterpreterState.ceval.own_gil is added in gh-104204).

We also add PyInterpreterState.ceval.own_gil to record if the interpreter actually has its own GIL.

Note that for now we don't actually respect own_gil; all interpreters still share the one GIL.  However, PyInterpreterState.ceval.own_gil does reflect PyInterpreterConfig.own_gil.  That lie is a temporary one that we will fix when the GIL really becomes per-interpreter.

* main:
  pythongh-99113: Add PyInterpreterConfig.own_gil (pythongh-104204)
  pythongh-104146: Remove unused var 'parser_body_declarations' from clinic.py (python#104214)
  pythongh-99113: Add Py_MOD_PER_INTERPRETER_GIL_SUPPORTED (pythongh-104205)
  pythongh-104108: Add the Py_mod_multiple_interpreters Module Def Slot (pythongh-104148)
  pythongh-99113: Share the GIL via PyInterpreterState.ceval.gil (pythongh-104203)
  pythonGH-100479: Add `pathlib.PurePath.with_segments()` (pythonGH-103975)
  pythongh-69152: Add _proxy_response_headers attribute to HTTPConnection (python#26152)
  pythongh-103533: Use PEP 669 APIs for cprofile (pythonGH-103534)
  pythonGH-96803: Add three C-API functions to make _PyInterpreterFrame less opaque for users of PEP 523. (pythonGH-96849)

…4206)

Py_MOD_PER_INTERPRETER_GIL_SUPPORTED is a new supported value for Py_mod_multiple_interpreters, added in gh-104205.

This is a pre-requisite for a per-interpreter GIL.  Without it this change isn't strictly necessary.  However, there is no real downside otherwise.