Teach TurboFan about representation changes from Float64 to Word64 where
the input value is already known to be within the Int64 or Uint64 range.
While not all of these values have representations in Float64, those
that do can be converted to Word64 without loss of precision.

Same is true for Tagged to Word64 conversions, although here we don't
(currently) need the case for Uint64 ranges, so we can skip adding an
operator for that until it becomes necessary (there's a hard check in
the code so it'll not silently cause trouble).

Bug: v8:8178
Change-Id: Ie99b0bc9af096bd927f63b26b0a61e66454bc4ae
Reviewed-on: https://chromium-review.googlesource.com/1231593Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56022}