RFR: 8320646: RISC-V: C2 VectorCastHF2F

[Hamlin Li]

Hi,
Can you review this patch to add instrinsics for VectorCastHF2F/VectorCastF2HF?
Thanks!

## Test

test/jdk/java/lang/Float/Binary16ConversionNaN.java
test/jdk/java/lang/Float/Binary16Conversion.java

hotspot/jtreg/compiler/intrinsics/float16
hotspot/jtreg/compiler/vectorization/TestFloatConversionsVectorjava
hotspot/jtreg/compiler/vectorization/TestFloatConversionsVectorNaN.java

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Commit messages:
 - fix jcheck error
 - clean code
 - Merge branch 'master' into float16-to-float-v
 - Refine tests
 - Initial commit: VectorCastF2HF
 - fix issues
 - fix widening vector register to even one
 - merge master
 - fix stub size
 - merge master
 - ... and 1 more: https://git.openjdk.org/jdk/compare/a18b03b8...521c2221

Changes: https://git.openjdk.org/jdk/pull/17698/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17698&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320646
  Stats: 360 lines in 9 files changed: 358 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17698.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17698/head:pull/17698

PR: https://git.openjdk.org/jdk/pull/17698