[lworld+fp16] RFR: 8329817: Augment prototype Float16 class [v3]

[Joe Darcy]

> Sketch of a more full-featured API for Float16.

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:

 - Add methods to Float16, use them in Float.
 - Update tests about merge.
 - Merge remote-tracking branch 'refs/remotes/origin/lworld+fp16' into JDK-8329817
 - Add @value tags to javadoc.
 - Adjust list of possible future work.
 - JDK-8329817: Augment prototype Float16 class

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Changes: https://git.openjdk.org/valhalla/pull/1117/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1117&range=02
  Stats: 628 lines in 4 files changed: 572 ins; 8 del; 48 mod
  Patch: https://git.openjdk.org/valhalla/pull/1117.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1117/head:pull/1117

PR: https://git.openjdk.org/valhalla/pull/1117