This adds missing support when converting a Word32 value (either in
Signed32 or Unsigned32 range) to Word64 representation, for which the
type also includes MinusZero. This conversion is fine as long as the
difference between 0 and -0 is not observable (in other words, as long
as the truncation identifies zeros).

Bug: chromium:971782, chromium:225811, v8:4153, v8:7881, v8:8171, v8:8383
Change-Id: I9d350a25f57b1342eb7fd1279d55a8610bdaf7cd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1664062Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62235}