Support building on JDK 21, and don't crash on JDK 21 bytecodes

[msridhar]

With these changes, WALA builds and runs on JDK 21, and our regression tests pass, except for the Dalvik tests. The Dalvik test issue is tracked as #1349. I think it's best to land these changes now, since they include important fixes for JDK 21 support. We can then fix Dalvik in a follow-up.

The main logic fix was to update the native models for java.lang.Thread to account for implementation changes there. Also there are a bunch of changes due to the deprecation of the URL(String) constructor.

[github-actions]

Test Results

   555 files  +100     555 suites  +100   3h 17m 39s ⏱️ + 42m 45s
   731 tests ±    0     714 ✔️ ±    0  17 💤 ±  0  0 ❌ ±0 
3 410 runs  +602  3 323 ✔️ +585  87 💤 +17  0 ❌ ±0 

Results for commit 22a1b6a. ± Comparison against base commit 7a13052.

♻️ This comment has been updated with latest results.

[msridhar]

Once this PR is approved, I will add the JDK 21 / ubuntu CI job as required before landing it.

[liblit]

I've been silently reviewing this PR's progress with each successive commit. That puts me in a position to approve this pull request now with little delay. Trust me that I have indeed looked over everything you're changing here.

[liblit]

Well done, @msridhar! 💪🧠

[msridhar]

Thanks for the quick review, @liblit! The Thread issue was a bit nasty to track down but the rest was thankfully straightforward.