[lworld+fp16] RFR: 8338061: Add support for FP16 unary and ternary operations [v2]

[Bhavana Kilambi]

> This patch adds support for three unary operators - abs, neg and sqrt and a ternary operator - fma for FP16.
> Both scalar and vector mid-end support along with aarch64 backend support are added.
> Tested all FP16 tests successfully on aarch64.

Bhavana Kilambi 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 three additional commits since the last revision:

 - Address review comments
 - Merge branch 'lworld+fp16'
 - 8338061: Add support for FP16 unary and ternary operations
   
   This patch adds support for three unary operators - abs, neg and sqrt
   and a ternary operator - fma for FP16.
   Both scalar and vector mid-end support along with aarch64 backend
   support are added.
   Tested all FP16 tests successfully on aarch64.

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1211/files
  - new: https://git.openjdk.org/valhalla/pull/1211/files/5d9b00f1..7538f860

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1211&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1211&range=00-01

  Stats: 527175 lines in 6068 files changed: 66213 ins; 122783 del; 338179 mod
  Patch: https://git.openjdk.org/valhalla/pull/1211.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1211/head:pull/1211

PR: https://git.openjdk.org/valhalla/pull/1211