[lworld] RFR: 8325106: [lworld] Part 3: Prepare compiler implementation and tests for JEP 401

[Tobias Hartmann]

A large number of leftover cleanups, enhancements and smaller fixes from the JEP 401 transition changes ([JDK-8324949](https://bugs.openjdk.org/browse/JDK-8324949), [JDK-8325660](https://bugs.openjdk.org/browse/JDK-8325660) and [JDK-8333037](https://bugs.openjdk.org/browse/JDK-8333037)). There are a few remaining issues but I filed separate bugs for those.

Thanks,
Tobias

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Commit messages:
 - More fixes
 - Removed unused code from PhaseMacroExpand::can_eliminate_allocation
 - Merge branch 'lworld' into JDK-8325106
 - Merge branch 'lworld' into JDK-8325106
 - And even more fixes
 - Aaand more fixes
 - More fixes
 - Putfield and buffering refactoring
 - Using C2_TIGHTLY_COUPLED_ALLOC
 - More changes
 - ... and 2 more: https://git.openjdk.org/valhalla/compare/8aa58dae...1b24eac9

Changes: https://git.openjdk.org/valhalla/pull/1189/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1189&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325106
  Stats: 359 lines in 25 files changed: 72 ins; 187 del; 100 mod
  Patch: https://git.openjdk.org/valhalla/pull/1189.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1189/head:pull/1189

PR: https://git.openjdk.org/valhalla/pull/1189