Phis act as proxys: a phi's input has only 32 bits observed iff
the phi's output has only 32 bits observed. When the Tagged Phi
has only 32 bits observed, the Phi's MachineRepresentation
changes to the Compressed counterpart.

Also, update machine graph verifier so that Phis of Compressed
accept Tagged inputs as well.

Bug: v8:7703
Change-Id: I365d0b38f76edbaecbfea29f603abd2ce2224878
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1879943Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64802}