Get rid of further typing checks from ChangeLowering and put them into
the representation selection pass instead (encoding the information in
the operator instead).

Drive-by-change: Rename ChangeSmiToInt32 to ChangeTaggedSignedToInt32
for consistency about naming Tagged, TaggedSigned and TaggedPointer.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1909343002

Cr-Commit-Position: refs/heads/master@{#35723}