We can constant-fold JSToNumber conversions during typed lowering
if the input is a known primitive constant (i.e. a string, oddball
or number). I.e. JSToNumber("123") can be constant-folded to 123.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1657213002

Cr-Commit-Position: refs/heads/master@{#33654}