[lworld+fp16] RFR: 8341245: Add 'shortest length' toString() to Float16 [v2]

[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:

  Revert back experimental remnant of valueOf(String).

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1260/files
  - new: https://git.openjdk.org/valhalla/pull/1260/files/18f09e6c..9b8a57b5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1260&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1260&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 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