This changes behavior of TurboFan to match the behavior of Crankshaft
when it comes to polymorphic loads of similar elements kind (i.e. all
tagged or all double), where we should use the "worst case" code without
a transition. This is often much faster than transitioning the elements
to the worst case first, trading a TransitionElementsKind for a CheckMaps
and avoiding mutation of the array.

This is beneficial for various crypto benchmarks, which don't need to
pay the cost for TransitionElementsKind now.

R=jarin@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2836943003
Cr-Commit-Position: refs/heads/master@{#44815}