[SYCL][Docs] Add sycl_ext_oneapi_virtual_mem extension and implementation (#8954)

This commit adds the sycl_ext_oneapi_virtual_mem experimental extension
for reserving and mapping virtual address ranges. Accompanying it is the
implementation in the SYCL runtime, together with CUDA and Level Zero
backend support for the corresponding features.

---------

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

Author: steffenlarsen

llvm/include/llvm/SYCLLowerIR/DeviceConfigFile.td

@@ -82,6 +82,7 @@ def AspectExt_intel_fpga_task_sequence : Aspect<"ext_intel_fpga_task_sequence">;
 def AspectExt_oneapi_limited_graph : Aspect<"ext_oneapi_limited_graph">;
 def AspectExt_oneapi_private_alloca : Aspect<"ext_oneapi_private_alloca">;
 def AspectExt_oneapi_queue_profiling_tag : Aspect<"ext_oneapi_queue_profiling_tag">;
+def AspectExt_oneapi_virtual_mem : Aspect<"ext_oneapi_virtual_mem">;
 // Deprecated aspects
 def AspectInt64_base_atomics : Aspect<"int64_base_atomics">;
 def AspectInt64_extended_atomics : Aspect<"int64_extended_atomics">;
@@ -139,7 +140,7 @@ def : TargetInfo<"__TestAspectList",
     AspectExt_oneapi_ballot_group, AspectExt_oneapi_fixed_size_group, AspectExt_oneapi_opportunistic_group,
     AspectExt_oneapi_tangle_group, AspectExt_intel_matrix, AspectExt_oneapi_is_composite, AspectExt_oneapi_is_component,
     AspectExt_oneapi_graph, AspectExt_intel_fpga_task_sequence, AspectExt_oneapi_limited_graph,
-    AspectExt_oneapi_private_alloca, AspectExt_oneapi_queue_profiling_tag],
+    AspectExt_oneapi_private_alloca, AspectExt_oneapi_queue_profiling_tag, AspectExt_oneapi_virtual_mem],
     []>;
 // This definition serves the only purpose of testing whether the deprecated aspect list defined in here and in SYCL RT
 // match.