Bug 1572644 - Part 4: Add WorkletLoadContext and nsMainThreadPtrHandle to delegate WorkletFetchHandler on the worklet thread. r=jonco,yulia

Add nsMainThreadPtrHandle to delegate WorkletFetchHandler.
Add WorkletLoadContext to wrap nsMainThreadPtrHandle.



Depends on D166541

Differential Revision: https://phabricator.services.mozilla.com/D166542

js/loader/ScriptLoadRequest.h

@@ -36,6 +36,7 @@ namespace mozilla::dom {
 
 class ScriptLoadContext;
 class WorkerLoadContext;
+class WorkletLoadContext;
 
 }  // namespace mozilla::dom
 
@@ -314,6 +315,8 @@ class ScriptLoadRequest
 
   mozilla::dom::WorkerLoadContext* GetWorkerLoadContext();
 
+  mozilla::dom::WorkletLoadContext* GetWorkletLoadContext();
+
   const ScriptKind mKind;  // Whether this is a classic script or a module
                            // script.