[lworld] RFR: 8376235: [lworld] analyze, clarify/organize and verify Valhalla ProblemLists

[Daniel D. Daugherty]

Trivial fixes to cleanup and/or remove Valhalla specific ProblemList entries.

I'm going to sprinkle the changes with links to JBS comments that explain
the changes in detail.

The view of the changes from the "Conversation" tab is often wrong with respect to which lines are changed.
The view of the changes from the "Files Changed" tab appears to be correct.

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Commit messages:
 - test/hotspot/jtreg/ProblemList-Virtual.txt - restore "Valhalla failures start here:" marker.
 - Merge branch 'lworld' into JDK-8376235
 - Disable ProblemList entry for vmTestbase/nsk/jdi/BScenarios/multithrd/tc04x001/TestDescription.java.
 - 8367590 is no longer reproducible.
 - 8304168 was resolved on 2024.03.30.
 - Five sub-tests in compiler/codegen/TestRedundantLea.java do not fail.
 - 8375470 was closed as a duplicate of 8247940
 - JDK-8365811 is resolved in jdk-26+12 on 2025.08.20.
 - Disable ProblemList entry for java/lang/Thread/virtual/stress/Skynet.java#default.
 - java/lang/ModuleLayer/LayerControllerTest.java and java/lang/ModuleLayer/BasicLayerTest.java fixed by jtreg7.5.
 - ... and 6 more: https://git.openjdk.org/valhalla/compare/d25325d3...48baceff

Changes: https://git.openjdk.org/valhalla/pull/2131/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376235
  Stats: 36 lines in 6 files changed: 2 ins; 30 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/2131.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2131/head:pull/2131

PR: https://git.openjdk.org/valhalla/pull/2131