x64 already had logic to enable a lower CPU extension if a higher
level one was supported. Add this to ia32. And also add SSSE3->SSE3
logic.

Drive-by cleanup to remove an extra CpuFeatureScope.

Bug: v8:11154
Change-Id: I12e3aa990cc07149da213911c624468a39f4e1a3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3212811Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77291}