Support NullAway `*.astubx` ?

[vorburger]

I've heard about (NullAway's) *.astubx format for the first time today, here - just so that I can find 😄 this again in the future, if ever:

• Add null safety check to Enola.dev build process enola-dev/enola#845 (comment)
• Hack NullAway LibraryModels generator MVP POC #2 (comment)
• External Annotations Format/s Support, instead LibraryModels uber/NullAway#1024 (comment)
• Tracking issue: making jspecify/jdk library models available to NullAway users uber/NullAway#950
• Repository for java.* annotation-overlay files, hosted/maintained by us jspecify/jspecify#25
• Search for astubx on NullAway

The goal of this issue is to see if a tool such as the one envisioned here should / could support this format...

FTR I'm probably not going to dig this into this any further, at least in the short term, this is more pro memoria. (If anything, I would probably play "directly" with (NullAway's) LibraryModels first; watch #2.)

/CC @cpovirk @msridhar FYI