Use tricky (NaN) values in SwizzleCopy and CopySlotsMasked

These are the last of the generic data-shuffling stage tests. Both of
these needed minor fixes to work with integer values, rather than
floats.

Change-Id: I4dc7382526c23862577b0bb49855f35a6d3b3dad
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/798407
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
4 files changed