Use unsigned values when constant-folding integer vectors

We already had this trick for scalar integers, this extends it to
integer vectors. As with prior work in this area, it would be better to
detect this case and produce an error, but now we at least produce
consistent and well-defined results (rather than undefined signed
integer overflow).

Bug: skia:10932
Bug: oss-fuzz:29494
Change-Id: I45526fe96b6ea42c0e88b9862f6961b316810321
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/363962
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
6 files changed