RFR: 8368822: Refactor Float16.valueOf(double) [v2]

[Joe Darcy]

> Refactoring to express the code more in terms of symbolic concepts rather than raw constants.

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

  Add overflow and underflow constants.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27540/files
  - new: https://git.openjdk.org/jdk/pull/27540/files/1ab238fd..a62df0f0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27540&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27540&range=00-01

  Stats: 16 lines in 1 file changed: 10 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/27540.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27540/head:pull/27540

PR: https://git.openjdk.org/jdk/pull/27540