[lworld+fp16] RFR: 8340013: x86 backend support for Float16 unary and ternary operations

[Jatin Bhateja]

Summary of changes:-
- Add optimized x86 backend implementation for scalar and vector flavors of following Float16 APIs.
  - FMA, SQRT, NEG, ABS
- Add memory operand patterns for all existing Float16 vector operations.

All existing Float16 functional and IR based tests are passing with the patch.

Best Regards,
Jatin

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Commit messages:
 - 8340013: x86 backend support for Float16 unary and ternary operations

Changes: https://git.openjdk.org/valhalla/pull/1243/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1243&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340013
  Stats: 374 lines in 7 files changed: 355 ins; 9 del; 10 mod
  Patch: https://git.openjdk.org/valhalla/pull/1243.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1243/head:pull/1243

PR: https://git.openjdk.org/valhalla/pull/1243