[vectorIntrinsics+fp16] RFR: 8302454: Improve VectorAPI fallback implementation for FP16 operations.

[Swati Sharma]

Hi All,

The patch contains the below changes:
- Remove redundant Halffloat object creation and rebase existing implementation using Float.float16ToFloat and floatToFloat16 APIs.
- Enable all the vector API tests for FP16 operations.

Please review and provide your feedback.

Thanks,
Swati

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Commit messages:
 - 8302454: Improve VectorAPI fallback implementation for FP16 operations.

Changes: https://git.openjdk.org/panama-vector/pull/211/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-vector&pr=211&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302454
  Stats: 8290 lines in 33 files changed: 7532 ins; 104 del; 654 mod
  Patch: https://git.openjdk.org/panama-vector/pull/211.diff
  Fetch: git fetch https://git.openjdk.org/panama-vector pull/211/head:pull/211

PR: https://git.openjdk.org/panama-vector/pull/211