[lworld] RFR: 8376430: [lworld] Remove Modifier.IDENTITY [v3]

[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 incrementally with one additional commit since the last revision:

  Fix identity modifier reference in getModifiers and accessFlags

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1980/files
  - new: https://git.openjdk.org/valhalla/pull/1980/files/78694ae8..44fd9e37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1980&range=02
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1980&range=01-02

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 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