Correctly discard or load RT when doing copies as draws in Vulkan

This fixes all the copy as draw issues we've had with certain devices and
the cap is no longer needed.

Bug: skia:
Change-Id: Id0b750849c4c920beae2d8cb3eda5f402018f194
Reviewed-On: https://skia-review.googlesource.com/114860
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-By: Brian Salomon <bsalomon@google.com>
Reviewed-on: https://skia-review.googlesource.com/115081
17 files changed