Double literals without dots should still be parsed as double constants,
not unsigned constants. The static_cast would remove the fractional
part, making constants like "1e-15" come out as "0" unsigned constants.

The precise semantics is not spec'ed, so we still consider literals like
"1e1" to be unsigned, and only switch to double if there is a fractional
part.

R=ecmziegler@chromium.org

Bug: chromium:1065635
Change-Id: I0aac018058a149632e0849572d19fdcc7b2af7aa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2126922Reviewed-by: Emanuel Ziegler <ecmziegler@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66949}