[lworld] RFR: 8328329: [lworld] Optimize field type checking sequence for x86 target.

[Jatin Bhateja]

- For field access bytecodes (getfield / putfield) interpreter perform special handling for flat / null restricted fields.
- Patch replaces existing flag checking sequence with efficient sequence based on 'bt' instruction.

Kindly review and approve.

Best Regards,
Jatin

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Commit messages:
 - 8328329: [lworld] Optimize field type checking sequence for x86 target.

Changes: https://git.openjdk.org/valhalla/pull/1051/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1051&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328329
  Stats: 20 lines in 3 files changed: 8 ins; 6 del; 6 mod
  Patch: https://git.openjdk.org/valhalla/pull/1051.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1051/head:pull/1051

PR: https://git.openjdk.org/valhalla/pull/1051