gh-107149: Rename PyUnstable_ExecutableKinds to _Py_ExecutableKinds

[vstinner]

Rename contants, replace Py with _Py (add underscore prefix):

• PY_EXECUTABLE_KIND_SKIP = > _PY_EXECUTABLE_KIND_SKIP
• PY_EXECUTABLE_KIND_PY_FUNCTION => _PY_EXECUTABLE_KIND_PY_FUNCTION
• PY_EXECUTABLE_KIND_BUILTIN_FUNCTION => _PY_EXECUTABLE_KIND_BUILTIN_FUNCTION
• PY_EXECUTABLE_KIND_METHOD_DESCRIPTOR => _PY_EXECUTABLE_KIND_METHOD_DESCRIPTOR
• PY_EXECUTABLE_KINDS => _PY_EXECUTABLE_KINDS

• Issue: C API: Rename _PyUnstable_GetUnaryIntrinsicName() to PyUnstable_GetUnaryIntrinsicName()? #107149

[gvanrossum]

Please hold off at least until we've had a change to discuss this with @markshannon. I expect see him tomorrow.

[vstinner]

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I rebased my PR on the main branch to re-trigger CI jobs.

[markshannon]

These constants are intended for tools like pyspy and austin, which are out-of-process tools.
They need to copy and paste the constants, so it doesn't matter to them whether they are private or unstable.
However, they could be useful for in-process tools as well, so making them "unstable" seems best.

Presumably that means moving them to Include/cpython/pyframe.h and giving them a PY_UNSTABLE prefix.

Generally, I think we shouldn't be adding private (ie. _PY_) constants to (semi-)public headers, unless we really can't avoid it.

[vstinner]

Presumably that means moving them to Include/cpython/pyframe.h and giving them a PY_UNSTABLE prefix.

Oh, I already wrote PR #108440 for that, the alternative option :-)

[vstinner]

@markshannon prefers to add this API to the public C API, so I close this PR. See PR #108440 instead.