RFR: 8341260: Add Float16 to jdk.incubator.vector [v8]

[Joe Darcy]

> Port of Float16 from java.lang in the lworld+fp16 branch to jdk.incubabor.vector.

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

  Improve specification per code review feedback.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21574/files
  - new: https://git.openjdk.org/jdk/pull/21574/files/ea7a72fa..96c05b5b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=06-07

  Stats: 19 lines in 1 file changed: 18 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21574.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21574/head:pull/21574

PR: https://git.openjdk.org/jdk/pull/21574