RFR: 8277489: Rewrite JAAS UnixLoginModule with FFM [v7]

[Weijun Wang]

> Rewrite the native calls with FFM.

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

  must have username; more comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28931/files
  - new: https://git.openjdk.org/jdk/pull/28931/files/b54ca67c..cfd794b8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28931&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28931&range=05-06

  Stats: 43 lines in 2 files changed: 5 ins; 25 del; 13 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