Add in f64x2 opcodes to simd scalar lowering, this allows us to enable
most of the f64x2 test cases with quite little changes - the significant
change is to make sure the comparisons return a Int64 node.

Bug: v8:10507
Change-Id: I8c8920d37c0cd0841dafcdb0310b6340b3c16189
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2399051Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69757}