RFR: 8357913: Add `@Stable` to BigInteger and BigDecimal [v4]

[Shaojin Wen]

> Some static final arrays of BigInteger and BigDecimal are stable and immutable. We should add `@Stable` to give the optimizer more information

Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into math_stable_202505
 - BigInteger::mag remove Stable
 - bug fix, from @minborg
 - BigInteger::mag add `@Stable`
 - add stable

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25437/files
  - new: https://git.openjdk.org/jdk/pull/25437/files/4e9be2c6..0edf6830

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25437&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25437&range=02-03

  Stats: 67304 lines in 1146 files changed: 37501 ins; 18443 del; 11360 mod
  Patch: https://git.openjdk.org/jdk/pull/25437.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25437/head:pull/25437

PR: https://git.openjdk.org/jdk/pull/25437