bpo-43795: Generate python3dll.c and doc data from manifest (PEP 652)

[encukou]

Here's an initial stab at PEP 652 – Maintaining the Stable ABI

There are two reviews I'm looking for:

1. The tool
   • I'm commandeering and assimilating Tools/scripts/stable_abi.py – @pablogsal, hope you're OK with that. I prefixed all the tool/platform-specific functions with gcc or binutils
   • The parser is recursive, which isn't necessary for this data set. But it will allow e.g. structs to have members that have their own data.
2. The contents of the limited API/stable ABI – this is definitely not final, but the diff in Doc/data/stable_abi.dat (the limited API) and PC/python3dll.c (Windows stable ABI) and the check-limited-api failure should show some juicy controversial items.

(Docs, tests and more file generators/checks to come later.)

https://bugs.python.org/issue43795

[encukou]

I anticipate discussions taking a while, so I also opened #25312 to reduce diffs for reviewers.

[pablogsal]

• The tool – I'm commandeering and assimilating Tools/scripts/stable_abi.py – @pablogsal, hope you're OK with that. I prefixed all the tool/platform-specific functions with gcc or binutils

👍 No problem, go ahead :)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @encukou for commit 89e86c9 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[encukou]

Despite some buildbots timing out os failing socket, I call this ready for review.