RFR: 8351565: Implement JEP 502: Stable Values (Preview) [v8]

[Per Minborg]

> Implement JEP 502.
> 
> The PR passes tier1-tier3 tests.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Revamp toString() methods

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/23972/files
  - new: https://git.openjdk.org/jdk/pull/23972/files/4c0dadfb..42d4dcfa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23972&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23972&range=06-07

  Stats: 173 lines in 14 files changed: 79 ins; 55 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/23972.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23972/head:pull/23972

PR: https://git.openjdk.org/jdk/pull/23972