Enable use of default platform context extension

If compiler supports default platform context extension, use that when building the cached.

Author: oleksandr-pavlyk

dpctl-capi/source/dpctl_sycl_device_manager.cpp

@@ -91,7 +91,13 @@ struct DeviceCacheBuilder
                 for (const auto &D : Devices) {
                     if (mRanker(D) < 0)
                         continue;
+#if defined(SYCL_EXT_ONEAPI_DEFAULT_CONTEXT)
+		    auto P = D.get_platform();
+		    auto DefaultCtx = P.ext_oneapi_get_default_context();
+		    auto entry = cache_l.emplace(D, DefaultCtx);
+#else
                     auto entry = cache_l.emplace(D, D);
+#endif
                     if (!entry.second) {
                         std::cerr << "Fatal Error during device cache "
                                      "construction.\n";