Add a performance debugging option that checkerboards sub-hierarchies that require a render target switch. #9473

We already have a debugging option that adds a checkerboard pattern to sub-hierarchies that have been rendered from a raster cache. Similarly, a debugging option that checkerboards sub-hierarchies that require a render target switch would be useful in diagnosing performance issues. For example, such an option would have easily enabled isolating the cause of this issue reported.

The naive way to do this would be add the checkerboard pattern every time we do an SkCanvas::saveLayer. However, we ended up doing the same for clips and such. In case of a stencil buffer and the items being axis aligned, it may be that the stencil buffer is used instead of a render target switch. So there needs to some investigation about how to get that information from Skia so that we don't report false positives.