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

[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.

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Commit messages:
 - 8338061: Add support for FP16 unary and ternary operations

Changes: https://git.openjdk.org/valhalla/pull/1211/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1211&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338061
  Stats: 1404 lines in 29 files changed: 636 ins; 5 del; 763 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