Avoid allocating a closure for ActivityMappingById.GetOrAdd if we can avoid it

Author: andrewlock

tracer/src/Datadog.Trace/Activity/Handlers/ActivityHandlerCommon.cs

@@ -176,15 +176,23 @@ public static void ActivityStarted<T>(string sourceName, T activity, OpenTelemet
                     return;
                 }
 
+#if NETCOREAPP
+                // Avoid closure allocation if we can
+                activityMapping = ActivityMappingById.GetOrAdd(
+                    activityKey.Value,
+                    static (_, details) => new(details.activity.Instance!, CreateScopeFromActivity(details.activity, details.tags, details.parent, details.traceId, details.spanId, details.rawTraceId, details.rawSpanId)),
+                    (activity, tags, parent, traceId, spanId, rawTraceId, rawSpanId));
+#else
                 activityMapping = ActivityMappingById.GetOrAdd(activityKey.Value, _ => new(activity.Instance!, CreateScopeFromActivity(activity, tags, parent, traceId, spanId, rawTraceId, rawSpanId)));
+#endif
             }
             catch (Exception ex)
             {
                 Log.Error(ex, "Error processing the OnActivityStarted callback");
                 activityMapping = default;
             }
 
-            static Scope CreateScopeFromActivity(T activity, ITags? tags, SpanContext? parent, TraceId traceId, ulong spanId, string? rawTraceId, string? rawSpanId)
+            static Scope CreateScopeFromActivity(T activity, OpenTelemetryTags? tags, SpanContext? parent, TraceId traceId, ulong spanId, string? rawTraceId, string? rawSpanId)
             {
                 var span = Tracer.Instance.StartSpan(
                     activity.OperationName,