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

[Raffaello Giulietti]

On Mon, 30 Sep 2024 15:48:12 GMT, Raffaello Giulietti <rgiulietti at openjdk.org> wrote:

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

_All_ possible `Float16` outputs are thoroughly tested (in about 1 s).

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PR Comment: https://git.openjdk.org/valhalla/pull/1260#issuecomment-2383583690