RFR: 8335922: Incorrect @Stable usage of LambdaForm$Name.index [v5]

[Chen Liang]

> The `@Stable` on the `index` field is incorrect, as stable only avoids inlining `0`. On a strategic view, this index field should just become final so that `Name` becomes eligible for value class migration once valhalla comes. This patch makes the `index` field final and updates the usages correspondingly.

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Update src/java.base/share/classes/java/lang/invoke/LambdaForm.java
  
  Co-authored-by: ExE Boss <3889017+ExE-Boss at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20178/files
  - new: https://git.openjdk.org/jdk/pull/20178/files/771755b1..9846703a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20178&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20178&range=03-04

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20178.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20178/head:pull/20178

PR: https://git.openjdk.org/jdk/pull/20178