We can select a better instruction for add+extmul, using one of the
multiply-long-accumulate instruction.

Define a helper struct to pattern match Add(x, OP(y, z)) and
Add(OP(x, y) z), and ensure that the matched OP is always on the
LHS, to simplify checking for matches.

Bug: v8:11548
Change-Id: I7ab488b262aa9f749785f973549ccd9fad72f4c8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2826725Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76708}