Added the comparison of two decompresses to the DecompressionElimination
AdvancedReducer. Note that it works in the case that lhs is equal to rhs.

Also added tests for its implementation.

Cq-Include-Trybots: luci.v8.try:v8_linux64_pointer_compression_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_linux64_arm64_pointer_compression_rel_ng
Bug: v8:8977, v8:7703
Change-Id: I21676a78b592859692768c3499ea11117d3bb5a5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1609793
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61647}