Liboffload image support

[RossBrunton]

Is your feature request related to a problem? Please describe

Adding (non-bindless) image support to liboffload for use in Unified Runtime and SYCL is going to be a non-trivial task. If we wanted to support it, we'd need to add an image handle API to liboffload (which so far only uses USM pointers) and probably add a CUArray equivalent to AMDGPU.

Since there's a push towards bindless images, another option is to mark this "legacy" images API as optional and not support it in liboffload.

Describe the solution you would like

For the following ur entry points:

• urMemImageCreate (and variants)
• urMemImageGetInfo
• urKernelSetArgSampler
• All sampler entry points

Either support them with the offload backend, or mark them as optional and have the offload backend return UNSUPPORTED.

Describe alternatives you have considered

No response

Additional context

No response

[RossBrunton]

So I made this issue and then discovered that apparently image support is actually currently optional in UR. It's just not documented very well. #20128 Hopefully should make it clearer, but keeping this issue open as a tracker for whether we want liboffload in particular to support images.