[jdk21u-dev] RFR: 8335922: Incorrect @Stable usage of LambdaForm$Name.index

[Roland Mesde]

Backporting JDK-8335922: Incorrect @Stable usage of LambdaForm$Name.index.

Updated all code that uses the ```index``` field to work with the new final modifier.

Ran GHA Sanity Checks (passed) and related tests (passed).

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Commit messages:
 - Backport aabec4a947ed2a808a1443fa6b2dabedd8c2dd9f

Changes: https://git.openjdk.org/jdk21u-dev/pull/2486/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2486&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335922
  Stats: 51 lines in 1 file changed: 4 ins; 28 del; 19 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2486.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2486/head:pull/2486

PR: https://git.openjdk.org/jdk21u-dev/pull/2486