In SkCanvas::clipRect, sort incoming rects

This makes our behavior more consistent with drawRect (where we always
sort rects). It also makes it more consistent between CPU and GPU. (CPU
used a technique to implement rect clipping that allowed for unsorted
rects, but GPU's clip stack would reject them as empty).

Fixes https://github.com/flutter/flutter/issues/38753

Change-Id: Ib91ebaf13d08dfe34105b9ee59021ac491d67bc7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317110
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>