[lworld] RFR: 8346035: javadoc value cleanup

[Roger Riggs]

Updated javadoc for value objects when preview is enabled.

Added text and decoration to highlight preview behavior of identity classes that are value classes with --enable-preview
The decorations are similar to the existing preview highlights for Preview classes and methods.

The updates include all of the wrapper classes, java.time, and java.util.Optional* and other classed annotated with @ValueBased.

The ValueBased is updated to describe the behavior when --enable-preview.

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Commit messages:
 - 8346035: [lworld] javadoc for value objects when enable preview
 - Edits to javadoc to clarify use when --enable-preview.

Changes: https://git.openjdk.org/valhalla/pull/1316/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1316&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346035
  Stats: 412 lines in 37 files changed: 255 ins; 3 del; 154 mod
  Patch: https://git.openjdk.org/valhalla/pull/1316.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1316/head:pull/1316

PR: https://git.openjdk.org/valhalla/pull/1316