[lworld+fp16] RFR: 8337605: Update description of constants in Float16

[Joe Darcy]

Align wording or Float16 constants more closely with wording used in Float/Double, add links to corresponding Float/Double constants.

-------------

Commit messages:
 - JDK-8337605: Update description of constants in Float16

Changes: https://git.openjdk.org/valhalla/pull/1191/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1191&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337605
  Stats: 37 lines in 1 file changed: 35 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1191.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1191/head:pull/1191

PR: https://git.openjdk.org/valhalla/pull/1191