Changes:
- Add LoopExit and LoopExitValue functions in wasm-compiler.
- Handle kLoopExitValue opcode in simd-scalar-lowering.

Bug: v8:11298
Change-Id: I4d00402ed1913f927bec973b3d480ddc1990962b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2611251Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72030}