In order to perform a blitFramebuffer operation, ANGLE uses
a compute shader which reads the stencil from a depth+stencil
image to a buffer, and then copies this buffer to the stencil
of the other image.

This cl basically treats VK_FORMAT_S8_UINT as VK_FORMAT_R8_UINT
with quad layout for the purpose of texture sampling.

Fixes the following tests:
dEQP-GLES3.functional.fbo.blit.depth_stencil.depth32f_stencil8_basic
dEQP-GLES3.functional.fbo.blit.depth_stencil.depth32f_stencil8_stencil_only
dEQP-GLES3.functional.fbo.blit.depth_stencil.depth24_stencil8_basic
dEQP-GLES3.functional.fbo.blit.depth_stencil.depth24_stencil8_stencil_only

Bug: b/142385547
Change-Id: Ib2ea7fa81496ceca1c24ea7f065b1c2cd05596ee
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/37188
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>