Wasm SIMD does not have an opcode to multiply a vector by a scalar. In
these cases, Wasm code uses mul(x, shuffle(y, imms)), where the shuffle
is a dup of a single lane in y. Pattern match on this to emit a fmul
(element).

We can do similar pattern match on f64x2 too, that will come in a future
patch.

Bug: v8:11257
Change-Id: I61e8c46b56719a1179c8a6032dbf8a4cc03b40a9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2719083
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73141}