[lworld] RFR: 8377714: [lworld] Re-enable virtual thread tests

[Patricio Chilano Mateo]

Please review the following patch which re-enables virtual thread tests `TestVirtualThreads.java`‎ and `Fuzz.java`.

First, this patch fixes the AArch64 virtual thread code to adapt to the changes in [JDK-8367151](https://bugs.openjdk.org/browse/JDK-8367151) where the valid FP is now stored in copy `#1` instead of copy `#2`:

https://github.com/openjdk/valhalla/blob/c0b679480a10bc9c71aa75ed26b3cfd0e69d294c/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp#L5960-L6007

With that change we can now simplify the `stackChunk` walking code and the thawing patching logic, since we don't need to keep track of two separate stack pointers, one to access the saved pc (`_unextended_sp[-1]`) and another to access the saved fp (`_sp[-2]`). Also, method `compiled_frame_details()` enables simplification of `FreezeBase::sender`.
Follow-up changes from [JDK-8371993](https://bugs.openjdk.org/browse/JDK-8371993) uncovered that in `ContinuationHelper::Frame::return_pc_address` we were reading the saved pc from the wrong location. This is also fixed in this PR. Going forward though, it seems the issue is with `f.real_fp()` which should include the extra added size for extended frames.

Second, the x64 code has been updated so that the layout of the extended frames is the same as with AArch64, and that we also only use the `#1` copies. This not only aligns behavior across both platforms but also allows simplification of the virtual thread code as mentioned above with AArch64. Changes in [JDK-8372806](https://bugs.openjdk.org/browse/JDK-8372806) uncovered the same issue with `ContinuationHelper::Frame::return_pc_address` and that is fixed as well.
Note: While working on this, I noticed that for extended frames, with `-XX:+PreserveFramePointer`, rbp is set to the location of copy `#2` rather than copy `#1`. Storing bad values in these locations will break the chain of pointers though, so we probably want to set rbp to location of copy `#1`. Same with AArch64.

Finally, for both AArch64 and x64 I updated `frame::describe_pd` to show correct locations of saved return pc and FP for extended frames. I still kept the locations where `#2` copies are stored. This has proven useful for debugging purposes.

Changes were tested by running both `TestVirtualThreads.java‎` and `Fuzz.java`, job `valhalla-comp-stress` in mach5, as well as tiers1-3. I also run `TestVirtualThreads.java‎` with extra flags, including `-Xcomp -XX:+SafepointALot -XX:+DeoptimizeALot` as reported in [JDK-8370177](https://bugs.openjdk.org/browse/JDK-8370177). This latter bug cannot be reproduced anymore after the assert was removed (JDK-8371993 for AArch64 and JDK-8372806 for x64), although it did uncovered a pre-existent issue in mainline which will be address by [JDK-8377715](https://bugs.openjdk.org/browse/JDK-8377715).

Thanks,
Patricio

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Commit messages:
 - v1

Changes: https://git.openjdk.org/valhalla/pull/2085/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2085&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377714
  Stats: 202 lines in 21 files changed: 66 ins; 74 del; 62 mod
  Patch: https://git.openjdk.org/valhalla/pull/2085.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2085/head:pull/2085

PR: https://git.openjdk.org/valhalla/pull/2085