The representation changer was lacking support for directly converting
Word64 values to Bit representation.

Bug: chromium:890243, v8:4153, v8:7881, v8:8171, v8:8178
Change-Id: I5fa31716c7b2b10ad00dc31d5035a1ada152661c
Reviewed-on: https://chromium-review.googlesource.com/1251551Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56304}