RFR: 8318598: FFM stylistic cleanups

[Jorn Vernee]

Port over stylistic changes from the panama-foreign repo. The following PRs are included:

- https://github.com/openjdk/panama-foreign/pull/863
- https://github.com/openjdk/panama-foreign/pull/888
- https://github.com/openjdk/panama-foreign/pull/889
- https://github.com/openjdk/panama-foreign/pull/893
- https://github.com/openjdk/panama-foreign/pull/894
- https://github.com/openjdk/panama-foreign/pull/897
- https://github.com/openjdk/panama-foreign/pull/906

Testing: `jdk_foreign`

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Commit messages:
 - Fix sonar issues and thread safety bug
 - Rename max alignment constants for heap segments
 - Modernize code
 - Fix typos
 - Fix the use of final and static
 - Remove unused imports
 - Clean up StringSupport

Changes: https://git.openjdk.org/jdk/pull/16286/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16286&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318598
  Stats: 310 lines in 34 files changed: 54 ins; 80 del; 176 mod
  Patch: https://git.openjdk.org/jdk/pull/16286.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16286/head:pull/16286

PR: https://git.openjdk.org/jdk/pull/16286