We were going for 64 bits to go back to 32 bits. For example,
TruncateInt64ToInt32(BitcastTaggedSignedToWord(ChangeCompressedToTagged(x)))
when that doesn't modify the value at all.

In order to keep the machine graph verifier happy two bitcast operations
were introduced.

As a drive-by nit cleanup, we were having two empty lines between some
functions implementations in machine-operator-reducer.cc.

Bug: v8:7703
Change-Id: Ifaa0d656010fe4f6f6f4581a2bb6633f060245b7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1749383
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63191}