Ensure that startup UI extensions are rendered correctly (#217)

UI extensions that should be active i.e. visible on startup might be activated to early (before the initial model loading is completed) which can cause rendering issues in some cases. This can be avoided by enabling these UI extensions after the model has been initialized.
(eclipse-glsp/glsp#585)

examples/workflow-standalone/src/app.ts

@@ -18,9 +18,9 @@ import {
     BaseJsonrpcGLSPClient,
     configureServerActions,
     EnableToolPaletteAction,
+    GLSPActionDispatcher,
     GLSPClient,
     GLSPDiagramServer,
-    IActionDispatcher,
     RequestModelAction,
     RequestTypeHintsAction,
     TYPES
@@ -56,7 +56,7 @@ async function initialize(connectionProvider: MessageConnection): Promise<void>
     });
     await configureServerActions(result, diagramType, container);
 
-    const actionDispatcher = container.get<IActionDispatcher>(TYPES.IActionDispatcher);
+    const actionDispatcher = container.get(GLSPActionDispatcher);
 
     await client.initializeClientSession({ clientSessionId: diagramServer.clientId, diagramType });
     actionDispatcher.dispatch(
@@ -68,6 +68,7 @@ async function initialize(connectionProvider: MessageConnection): Promise<void>
         })
     );
     actionDispatcher.dispatch(RequestTypeHintsAction.create());
+    await actionDispatcher.onceModelInitialized();
     actionDispatcher.dispatch(EnableToolPaletteAction.create());
 }