RFR: 8341260: Add Float16 to jdk.incubator.vector [v3]

[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 seven additional commits since the last revision:

 - 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
 - Add support for BigDecimal -> Float16 conversion.
 - JDK-8341260: Add Float16 to jdk.incubator.vector

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21574/files
  - new: https://git.openjdk.org/jdk/pull/21574/files/18c986db..0328e217

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21574&range=01-02

  Stats: 4055 lines in 104 files changed: 3381 ins; 486 del; 188 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