[lworld+fp16] RFR: 8341245: Add 'shortest length' toString() to Float16 [v3]

[Raffaello Giulietti]

> Add `Float16.toString()` with the same 'shortest length' properties as of `[Double|Float].toString()`.

Raffaello Giulietti has updated the pull request incrementally with one additional commit since the last revision:

  Addressing review comments.

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1260/files
  - new: https://git.openjdk.org/valhalla/pull/1260/files/9b8a57b5..f2dc5685

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1260&range=02
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1260&range=01-02

  Stats: 150 lines in 5 files changed: 126 ins; 2 del; 22 mod
  Patch: https://git.openjdk.org/valhalla/pull/1260.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1260/head:pull/1260

PR: https://git.openjdk.org/valhalla/pull/1260