RFR: 8370666: VectorAPI: Add clear comments for vector relative code in c2 [v2]

[Xiaohong Gong]

> The VectorMask implementation in Vector API involves complex interactions between types, nodes, and platform-specific
> features, making the related code in HotSpot difficult to understand and review.
> 
> This patch adds comprehensive comments for vector mask related types, nodes, and methods in C2 to improve code clarity and
> maintainability.
> 
> Note: This patch only adds comments; no functional changes are made.

Xiaohong Gong has updated the pull request incrementally with one additional commit since the last revision:

  Add more comments for vector nodes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29130/files
  - new: https://git.openjdk.org/jdk/pull/29130/files/ed5e79f7..6782b7f6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29130&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29130&range=00-01

  Stats: 227 lines in 1 file changed: 54 ins; 130 del; 43 mod
  Patch: https://git.openjdk.org/jdk/pull/29130.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29130/head:pull/29130

PR: https://git.openjdk.org/jdk/pull/29130