[SYCL][Docs] Add get_native_context call to interop_handle example (#16901)

The interop_handle example in the L0 backend specification uses a L0
context handle, but it may be unclear to users how that context handle
is accessible. Since it needs to be at least associated with the
corresponding device, it seems proper to be explicit in the example
about how to get it from the interop_handle.

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/doc/extensions/supported/sycl_ext_oneapi_backend_level_zero.md

@@ -300,6 +300,8 @@ data to the host to access the data. Users can get type of the allocation using
     Queue.submit([&](handler &CGH) {
         auto BufferAcc = Buffer.get_access<access::mode::write>(CGH);
         CGH.host_task([=](const interop_handle &IH) {
+            ze_context_handle_t ZeContext =
+                IH.get_native_context<backend::ext_oneapi_level_zero>();
             void *DevicePtr =
                 IH.get_native_mem<backend::ext_oneapi_level_zero>(BufferAcc);
             ze_memory_allocation_properties_t MemAllocProperties{};