VkImage use different structures to represent subregions:
- VkImageSubresource (Single mip level, single layer)
- VkImageSubresourceLayers (Single mip level, multiple layers)
- VkImageSubresourceRange (Multiple mip levels, multiple layers)

This cl changes the subregion structure used in vk::Image and in the
Blitter so that it contains the information required for the current
task and no more than that.

Bug: b/159045555
Change-Id: I186a90ff321318319c01a0718a95bbae2d2eb26a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/45788
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>