RFR: 8341260: Add Float16 to jdk.incubator.vector [v7]

[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 12 additional commits since the last revision:

 - 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.
 - Update with changes from lworld+fp16 Float16.
 - Merge branch 'master' into JDK-8341260
 - ... and 2 more: https://git.openjdk.org/jdk/compare/fe134ef4...ea7a72fa

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21574/files
  - new: https://git.openjdk.org/jdk/pull/21574/files/be72e76e..ea7a72fa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=05-06

  Stats: 91884 lines in 153 files changed: 87918 ins; 3576 del; 390 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