First simple implementation of image blitting.
Note that layers are not yet taken into account.

Passes almost all tests in (There are only 2 failures,
which both have an off by 1 error on a single pixel):
dEQP-VK.api.copy_and_blit.core.blit_image.simple_tests.*

Bug b/118619338 b/119620767

Change-Id: I1e0ac88089d6159924569099ea6345804a219d2c
Reviewed-on: https://swiftshader-review.googlesource.com/c/23268Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>