move `_Py_unicode_state.ids` (`_Py_Identifier`) into `_PyRuntimeState.global_objects.singletons`

[ericsnowcurrently]

[ericsnowcurrently]

python/cpython#30131

(for https://bugs.python.org/issue46006)

[ericsnowcurrently]

The underlying problem code was reverted in gh-30422. So I'll need to adjust the PR I have up.

[ericsnowcurrently]

I've tabled #176, but a form of this task is probably still worth doing, for the sake of the overlap with "deepfreeze". (See #218.)

[ericsnowcurrently]

If #230 works out, this issue is unnecessary.

[ericsnowcurrently]

I'm closing this as it's so low priority at this point that it doesn't need to be on our board.