RFR: 8338023: Support two vector selectFrom API [v6]

[Jatin Bhateja]

On Tue, 27 Aug 2024 20:00:56 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

> My comment was related to understanding what `SelectFromTwoVectorNode::Ideal` and `VectorRearrangeNode::Ideal` are doing - the former lowers, if needed, into the rearrange expression and the latter adjusts, if needed, the index vector (a comment describing this transformation would be useful, like you have in the former method).

Done.

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PR Comment: https://git.openjdk.org/jdk/pull/20508#issuecomment-2316759572