[lworld+fp16] RFR: 8339473: Add support for FP16 isFinite, isInfinite and isNaN

[Bhavana Kilambi]

This patch adds intrinsic support for FP16 isNaN, isFinite and isInfinite methods and also adds aarch64 backend for these intrinsics.

Tested all FP16 related tests successfully on aarch64.

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Commit messages:
 - 8339473: Add support for FP16 isFinite, isInfinite and isNaN

Changes: https://git.openjdk.org/valhalla/pull/1239/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1239&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339473
  Stats: 832 lines in 15 files changed: 198 ins; 0 del; 634 mod
  Patch: https://git.openjdk.org/valhalla/pull/1239.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1239/head:pull/1239

PR: https://git.openjdk.org/valhalla/pull/1239