RFR: 8359119: Change Charset to use StableValue

[Per Minborg]

On Tue, 10 Jun 2025 14:09:03 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> Fields and methods can better leverage the Stable Value API compared to using DCL and holder classes. There are also some fields that can be marked `@Stable`.
> 
> This PR passes tier1, tier2, and tier3 tests on multiple platforms.

Current startup performance on an M1 macOS using `brr -b perfstartup-noop`.

Base:

Wall clock:       29.5 ms/op
  :.cycles:       100702748 average cycles elapsed
  :.instructions: 196311919 average instructions retired
  :.maxrss:       39100416 bytes maximum resident set size
  :.taskclock:    23.0 ms/op

  
Patch:

Wall clock:       29.0 ms/op
  :.cycles:       101696210 average cycles elapsed
  :.instructions: 196761541 average instructions retired
  :.maxrss:       39067648 bytes maximum resident set size
  :.taskclock:    22.5 ms/op

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PR Comment: https://git.openjdk.org/jdk/pull/25727#issuecomment-2959567453