[lworld+fp16] RFR: 8329817: Augment prototype Float16 class [v12]

[Joe Darcy]

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

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Refactor code, refine spec, add tests.

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1117/files
  - new: https://git.openjdk.org/valhalla/pull/1117/files/619a031d..553b9325

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1117&range=11
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1117&range=10-11

  Stats: 283 lines in 2 files changed: 186 ins; 31 del; 66 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