RFR: 8370666: VectorAPI: Add clear comments for vector relative code in c2 [v3]

[Xiaohong Gong]

On Fri, 16 Jan 2026 09:28:49 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Thanks for looking at this PR. I added the mask type comment  at the IR definition code in `vectornode.hpp` for these two IRs. Is that fine to you? Or we'd better comment here as well.
>
> A mention here will complete the link b/w B and N/P representations.

Ok. I will add it with next commit. Thanks for your suggestion!

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PR Review Comment: https://git.openjdk.org/jdk/pull/29130#discussion_r2697685857