[lworld] RFR: 8321941: Migrate test/jdk/valhalla/valuetypes from primitive classes to null-restricted types

[Mandy Chung]

Migrate test/jdk/valhalla/valuetypes tests to use null-restricted types instead.

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Commit messages:
 - more clean up
 - clean up
 - Migrate tests to value types (part 2)
 - Replace Unsafe::getNullRestrictedReference and call zeroInstance directly in LF
 - Migrate libraries tests to null-restricted (part 1)

Changes: https://git.openjdk.org/valhalla/pull/963/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=963&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321941
  Stats: 3600 lines in 37 files changed: 475 ins; 2645 del; 480 mod
  Patch: https://git.openjdk.org/valhalla/pull/963.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/963/head:pull/963

PR: https://git.openjdk.org/valhalla/pull/963