[SYCL][Graph] L0 Backend support for SYCL Graphs (2/4) (intel#9992)

# Level Zero Backend Support for SYCL Graphs
This is the second patch of a series that adds support for an
[experimental command graph
extension](intel#5626)

A snapshot of the complete work can be seen in draft PR intel#9375 which has
support all the specification defined ways of
adding nodes and edges to the graph, including both Explicit and Record
& Replay graph construction. The two types of nodes currently
implemented are kernel execution and memcpy commands.

See https://github.com/reble/llvm#implementation-status for the status
of our total work.

## Scope
This second patch focuses on the required PI/UR support for the
experimental command-buffer feature in the Level Zero adapter:
* PI stubs for all adapters to enable compilation, no functionality.
* Command-buffer implementation for the Level Zero UR adapter.
* Stubs for the CUDA UR adapter to enable compilation, no functionality.

## Following Split PRs
Future follow-up PRs with the remainder of our work on the extension
will include:
* Hooking up backend to graphs runtime, bugfixes and other feature
additions, will add symbols but not break the ABI. (3/4)
* Add end-to-end tests for SYCL Graph extension. (4/4)
* NFC changes - Design doc and codeowner update.

## Authors
Co-authored-by: Pablo Reble <[email protected]>
Co-authored-by: Julian Miller <[email protected]>
Co-authored-by: Ben Tracy <[email protected]>
Co-authored-by: Ewan Crawford <[email protected]>
Co-authored-by: Maxime France-Pillois
<[email protected]>

---------

Co-authored-by: Ewan Crawford <[email protected]>
Co-authored-by: Maxime France-Pillois <[email protected]>