[SYCL][Graph] Add spec wording for graph-owned memory allocations (#18001)

- Using
[sycl_ext_codeplay_async_memory_alloc](intel/llvm#14800)
extension (PR currently in review)
- Spec wording for graph support of the feature
- Usage guide guidance for library authors
- Usage guide examples of explicit and queue recording usage with and
without mem pools

Author: Bensuo