[lworld] RFR: 8376427: [lworld] Mark Strict Fields APIs as part of Strict Fields JEP

[Chen Liang]

The strict fields APIs should be marked as under strict fields JEP. Javadoc would then correctly filter them in the preview page.  Also did some other javadoc and implementation cleanup (related to previous merges mostly)

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Commit messages:
 - Add strict fields JEP to javadoc

Changes: https://git.openjdk.org/valhalla/pull/1978/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1978&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376427
  Stats: 32 lines in 6 files changed: 18 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/valhalla/pull/1978.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1978/head:pull/1978

PR: https://git.openjdk.org/valhalla/pull/1978