feat(segmentation): Add customization for handling missing referencedDisplaySetInstanceUID for the SEG/RTSTRUCT. (#4983)

extensions/default/src/customizations/missingReferenceDisplaySetHandler.ts

@@ -0,0 +1,5 @@
+export default {
+  missingReferenceDisplaySetHandler: () => {
+    return Promise.resolve({ handled: false });
+  },
+};