Copying compressed images is just a matter of taking
block size into account and using a block as a single
unit of measure, instead of using a texel.

Bug b/119620767

Tests: dEQP-VK.api.copy_and_blit.core.image_to_image.all_formats.color.*

Change-Id: Ie77defc197ac7abb09a8555b384093fd50be681b
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28048Tested-by: Alexis Hétu <sugoi@google.com>
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>