RFR: 8321021: RISC-V: C2 VectorUCastB2X

[Hamlin Li]

Hi,
Can you help to review the patch to add support for some vector intrinsics?
Also complement various tests on riscv.
Thanks.

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Commit messages:
 - clean code
 - add more tests
 - rearrange tests layout
 - merge master
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/18040/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18040&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321021
  Stats: 715 lines in 6 files changed: 666 ins; 14 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/18040.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18040/head:pull/18040

PR: https://git.openjdk.org/jdk/pull/18040