RFR: 8335922: Incorrect @Stable usage of LambdaForm$Name.index [v4]

[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 four additional commits since the last revision:

 - Make LambdaForm.Name index final
 - Revert "8335922: Incorrect stable usage of LambdaForm$Name.index"
   
   This reverts commit 7d111ba3655c4c282399a4793e2cf5d91618432f.
 - Revert "We have sufficient space in short, use +1 offset"
   
   This reverts commit 0743c5f924fa07ea13f8545604f870091fa8d23a.
 - Revert "Encapsulate offsetIndex, share computation result"
   
   This reverts commit db805834d7117e5752bebcbd671afa6c85ff2cf0.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20178/files
  - new: https://git.openjdk.org/jdk/pull/20178/files/db805834..771755b1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20178&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20178&range=02-03

  Stats: 65 lines in 2 files changed: 4 ins; 30 del; 31 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