Replace SkImage_Base::view() and ::refView() with new asView().

Make SkImage_Gpu and SkImage_GpuYUVA have their own implementations
rather than sharing one in SkImage_GpuBase.

New function takes a GrImageTexGenPolicy to enable caller to
force a new texture to be made and choose it's budgeting status rather
than receive a cached view or a view owned by the image.

It also communicates any color type changes when converting a non-
texture image to a texture.

Bug: skia:11208
Change-Id: I6b389442bf9752276a83b21021070e3190610cd7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/361356
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
26 files changed