Turn the retyping pass of SimplifiedLowering into a proper phase, and
make it possible to propagate feedback types through non-speculative
operators. This defers the output representation selection to the
retyping phase, and checks that we don't mess up.

As a first user, we consume input type feedback for NumberAbs as well.
Long-term we can add all other operators to the mix.

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2139203002
Cr-Commit-Position: refs/heads/master@{#37672}