[lworld] RFR: 8280979: [lworld] Rename PrimitiveObjectMethods to ValueObjectMethods

[Mandy Chung]

This PR does the renaming to match the Value Objects JEP.

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Commit messages:
 - 8280979: Rename PrimitiveObjectMethods to ValueObjectMethods

Changes: https://git.openjdk.org/valhalla/pull/787/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=787&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8280979
  Stats: 999 lines in 14 files changed: 494 ins; 479 del; 26 mod
  Patch: https://git.openjdk.org/valhalla/pull/787.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/787/head:pull/787

PR: https://git.openjdk.org/valhalla/pull/787