gh-114940: Add _Py_FOR_EACH_TSTATE_UNLOCKED(), and Friends

[ericsnowcurrently]

This is a precursor to the actual fix for gh-114940, where we will change these macros to use the new lock. This change is almost entirely mechanical; the exceptions are the loops in codeobject.c and ceval.c, which now hold the "head" lock. Note that almost all of the uses of _Py_FOR_EACH_TSTATE_UNLOCKED() here will change to _Py_FOR_EACH_TSTATE_BEGIN() once we add the new per-interpreter lock.

[ericsnowcurrently]

@colesbury, do you have any objections to how I turn _Py_FOR_EACH_THREAD() into _Py_FOR_EACH_STW_INTERP() in pystate.c? Again, it's a fairly mechanical change, but it will allow us to more easily switch to the per-interpreter lock in a follow-up PR.

[colesbury]

No objections from me!