Reland of "TransitionArray now uses <is_data_property, name, attributes> tuple as a key, which allows to have several entries for the same property name."

Review URL: https://codereview.chromium.org/793453004

Cr-Commit-Position: refs/heads/master@{#25750}
Make loop assignment analysis a separate phase.

R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/770373003

Cr-Commit-Position: refs/heads/master@{#25751}