Port e607e12e

Original commit message:
    Introduce a new machine operator Float64Pow that for now is backed by
    the existing MathPowStub to start the unification of Math.pow, and at
    the same time address the main performance issue that TurboFan still has
    with the imaging-darkroom benchmark in Kraken.

    Also migrate the Math.pow builtin itself to a TurboFan builtin and
    remove a few hundred lines of hand-written platform code for special
    handling of the fullcodegen Math.pow version.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=v8:3599,v8:5086,v8:5157
LOG=N

Review-Url: https://codereview.chromium.org/2106883002
Cr-Commit-Position: refs/heads/master@{#37344}