[UR][L0v2] basic host tasks implementation

[pbalcer]

WIP...

Right now this is gated behind UR_HOST_TASK=1. SYCL changes are there just for testing. I'm not sure how it will end up looking like.

Known limitations:

• Accessing USM shared memory isn't allowed inside of a host task.
• Using L0 or UR API inside of a host task is UB (so no sycl host_task interop)

[pbalcer]

ping @slawekptak

[sarnex]

i think this is causing hangs on windows bmg, i cancelled the job, please make sure it's solved before running CI again, thanks!