RFR: 8277489: Rewrite JAAS UnixLoginModule with FFM [v8]

[Weijun Wang]

> Rewrite the native calls with FFM.

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  new naming style; use VarHandle to access fields

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28931/files
  - new: https://git.openjdk.org/jdk/pull/28931/files/cfd794b8..bf91106e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28931&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28931&range=06-07

  Stats: 36 lines in 1 file changed: 1 ins; 6 del; 29 mod
  Patch: https://git.openjdk.org/jdk/pull/28931.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28931/head:pull/28931

PR: https://git.openjdk.org/jdk/pull/28931