Adopt activationEventsGenerator for custom editors (microsoft#166718)

For microsoft#166624

Author: mjbvz

src/vs/workbench/contrib/customEditor/browser/customEditor.contribution.ts

@@ -29,9 +29,7 @@ Registry.as<IEditorPaneRegistry>(EditorExtensions.EditorPane)
 	]);
 
 Registry.as<IEditorFactoryRegistry>(EditorExtensions.EditorFactory)
-	.registerEditorSerializer(
-		CustomEditorInputSerializer.ID,
-		CustomEditorInputSerializer);
+	.registerEditorSerializer(CustomEditorInputSerializer.ID, CustomEditorInputSerializer);
 
 Registry.as<IWorkbenchContributionsRegistry>(WorkbenchExtensions.Workbench)
 	.registerWorkbenchContribution(ComplexCustomWorkingCopyEditorHandler, LifecyclePhase.Starting);

src/vs/workbench/contrib/customEditor/common/extensionPoint.ts

@@ -89,5 +89,13 @@ const CustomEditorsContribution: IJSONSchema = {
 export const customEditorsExtensionPoint = ExtensionsRegistry.registerExtensionPoint<ICustomEditorsExtensionPoint[]>({
 	extensionPoint: 'customEditors',
 	deps: [languagesExtPoint],
-	jsonSchema: CustomEditorsContribution
+	jsonSchema: CustomEditorsContribution,
+	activationEventsGenerator: (contribs: ICustomEditorsExtensionPoint[], result: { push(item: string): void }) => {
+		for (const contrib of contribs) {
+			const viewType = contrib[Fields.viewType];
+			if (viewType) {
+				result.push(`onCustomEditor:${viewType}`);
+			}
+		}
+	},
 });