Refactor HWUI readback code to be backend independent

Implement readback from Surface, TextureView and HW Bitmap
for Vulkan pipeline by wrapping the graphics buffer in an SkImage.
Refactor both Vulkan and GL readback to use common code.
TextureView readback is moved from IRenderPipeline interface to
Readback class. Refactor all 3 readback flows to use common
implementation.

Test: Passed all view, uirendering and graphics CTS tests with GL
Test: Passed many CTS test with Vulkan, that require readback
Bug: 113673613
Change-Id: Ifbfd8170a5401f87a709b4b1b9fa058e8e11768d