Add a dedicated operator for ToNumber(x) with feedback instead of
translating to SpeculativeNumberMultiply(x,1), which allows us to
treat the case where x is already a Number specially, ignoring the
feedback on the operator. This recovers most of the regression in
the crypto benchmark.

BUG=chromium:709398,v8:6214,v8:5267
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2802113003
Cr-Commit-Position: refs/heads/master@{#44484}