Liboffload image support

### 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](https://oneapi-src.github.io/unified-runtime/core/api.html#urmemimagecreate) (and variants)
* [urMemImageGetInfo](https://oneapi-src.github.io/unified-runtime/core/api.html#urmemimagegetinfo)
* [urKernelSetArgSampler](https://oneapi-src.github.io/unified-runtime/core/api.html#urkernelsetargsampler)
* [All sampler entry points](https://oneapi-src.github.io/unified-runtime/core/api.html#sampler)

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_