[vectorIntrinsics+fp16] RFR: 8290204: FP16 initial backend implementation [v6]

[Smita Kamath]

> Initial backend implementation for enabling FP16.

Smita Kamath has updated the pull request incrementally with three additional commits since the last revision:

 - Correction in HF2D node
 - typo in D2HF node
 - Updated cast instructs with new nodes

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Changes:
  - all: https://git.openjdk.org/panama-vector/pull/204/files
  - new: https://git.openjdk.org/panama-vector/pull/204/files/831b266e..a19f869d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-vector&pr=204&range=05
 - incr: https://webrevs.openjdk.org/?repo=panama-vector&pr=204&range=04-05

  Stats: 124 lines in 7 files changed: 114 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/panama-vector/pull/204.diff
  Fetch: git fetch https://git.openjdk.org/panama-vector pull/204/head:pull/204

PR: https://git.openjdk.org/panama-vector/pull/204