Vulkan: Fix copyImage region parameters. In cases where we were reading back more than one pixel in ReadPixels, and in some cases for texture init, we weren't using the correct parameters to vkCmdCopyImage. This CL fixes both of those by using more correct copy regions, and fixing the row and depth pitch computation using vkGetImageSubresourceLayout. BUG=angleproject:2167 Change-Id: Ib70217ed4a17be6b4b1b8aeec9a8a6199d210d88 Reviewed-on: https://chromium-review.googlesource.com/732190 Reviewed-by: Frank Henigman <fjhenigman@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>