RFR: 8295555: Primitive wrapper caches could be `@Stable`

[Per Minborg]

This PR proposes adding `@Stable` to certain wrapper classes' cache arrays (e.g. `Integer` and `Long`).

Comments are welcome as to how to improve the VM's handling now that the backing cache array is `@Stable`. Are there simplifications to be made or are there other optimizations we might add?

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Commit messages:
 - Fix trailing white spaces
 - Reinsert row
 - Annotate CharacterCache @Stable
 - Mark caching arrays @Stable

Changes: https://git.openjdk.org/jdk/pull/14418/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14418&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295555
  Stats: 16 lines in 5 files changed: 11 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/14418.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14418/head:pull/14418

PR: https://git.openjdk.org/jdk/pull/14418