[lworld] RFR: 8376430: [lworld] Remove Modifier.IDENTITY [v2]

[Chen Liang]

> `java.lang.reflect.Modifier` represents Java language modifiers. Since a previous iteration of JEP 401, the "identity" source modifier is removed, and only "value" source modifier exists. As a result, "identity" is no longer qualified to be present in `Modifier`. We should migrate all its uses to `ClassFile.ACC_IDENTITY` or `AccessFlag.IDENTITY` (which already correctly identifies itself not as a source modifier).
> 
> This also avoids the headache of `Modifier.toString` clashing over `SYNCHRONIZED` versus `IDENTITY`.

Chen Liang 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 three additional commits since the last revision:

 - Refer to access flag presence per Joe
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into fix/remove-modifier-identity
 - Purge Modifier.IDENTITY

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1980/files
  - new: https://git.openjdk.org/valhalla/pull/1980/files/48a3a442..78694ae8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1980&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1980&range=00-01

  Stats: 806 lines in 80 files changed: 429 ins; 170 del; 207 mod
  Patch: https://git.openjdk.org/valhalla/pull/1980.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1980/head:pull/1980

PR: https://git.openjdk.org/valhalla/pull/1980