We currently have three different compresses that we thought it could be
a good idea to merge into only one. Merging them would make sense since
they all end up with the same code being generated. However, we would be
losing knowing the MachineRepresentation in the cases of CompressSigned
and Pointer.

For example, in machine-graph-verifier everything will have to be
MachineRepresentation::kCompressed
https://cs.chromium.org/chromium/src/v8/src/compiler/machine-graph-verifier.cc?l=226

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: I244e2e61cab2bb87830bc0aabdbe5e43f243b424
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1624798Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61882}