Image objects now have the ability to copy their content to another
image object. They can also copy their content to or from Buffer
objects.

Bug b\119620767

Change-Id: I047e9ecdcc11e264589de1d9461ef448f22a4d9e
Reviewed-on: https://swiftshader-review.googlesource.com/c/23070Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>