xgl: Add xglCmdBlitImage entry point
xgl: Add xglCmdBlitImage entry point

Rebase updates
Part one of adding support for abitrary scaled blits and format conversions.
Just interface here. Functionality to follow.
bug #13071
alpha rev: r29665

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools