RFR: 8341260: Add Float16 to jdk.incubator.vector [v9]

[Joe Darcy]

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

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 14 additional commits since the last revision:

 - Merge branch 'master' into JDK-8341260
 - Improve specification per code review feedback.
 - Add tests, improve hashing spec.
 - Merge branch 'master' into JDK-8341260
 - Add equals/hashCode implementation; tests to follow.
 - Respond to review feedback.
 - Respond to review feedback.
 - Add @since tag, respond to review feedback.
 - Merge branch 'master' into JDK-8341260
 - Remove comments for intrinsics per review feedback.
 - ... and 4 more: https://git.openjdk.org/jdk/compare/5424e7d7...064c2784

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21574/files
  - new: https://git.openjdk.org/jdk/pull/21574/files/96c05b5b..064c2784

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=07-08

  Stats: 107270 lines in 273 files changed: 6033 ins; 99611 del; 1626 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