Return an empty object for RCTVirtualText from DummyUIManager

Summary:
We currently use `UIManager.getViewManagerConfig()` in a few places to check if a view manager exists at runtime; right now these checks fail for Venice because our DummyUIManager returns null. We don't yet have a replacement for this API for Fabric (see T59411524) so for now let's just hard code the view managers that we know exist to return something truthy here. This is hacky, but it works ok for now.

Changelog: [Internal]

Reviewed By: PeteTheHeat

Differential Revision: D19185957

fbshipit-source-id: e3135b45db4c9ff27fd95362deaa3c1b4340bf48

Libraries/ReactNative/DummyUIManager.js

@@ -11,10 +11,13 @@
 'use strict';
 
 module.exports = {
-  getViewManagerConfig: (viewManagerName: string): null => {
+  getViewManagerConfig: (viewManagerName: string): mixed => {
     console.warn(
       'Attempting to get config for view manager: ' + viewManagerName,
     );
+    if (viewManagerName === 'RCTVirtualText') {
+      return {};
+    }
     return null;
   },
   getConstants: (): {...} => ({}),