RFR: 8332153: RISC-V: enable tests and add comment for vector shift instruct (shared by vectorization and Vector API) [v2]

[Hamlin Li]

> Hi,
> Can you help to review this patch?
> For vector shift instruct, some corresponding tests are not enabled, this is to enable them.
> And the way how vector shift instruct works is not clear, especially both vectorization (SLP in jdk) and Vector API share the same instruct's in riscv_v.ad, so also added some comment to clarify it.
> 
> Thanks

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  fix words

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/19265/files
  - new: https://git.openjdk.org/jdk/pull/19265/files/0078c854..809f92e9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19265&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19265&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19265.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19265/head:pull/19265

PR: https://git.openjdk.org/jdk/pull/19265