Introduce static resource URLs

Summary: Introduced an API that converts a filepath, relatively to the `desktop/static/` folder in a url that can be resolved by the render environment. This will generate `file://` urls in Electron, and root relative `/` urls in browser envs

Reviewed By: aigoncharov

Differential Revision: D32767427

fbshipit-source-id: 378da7709bcb19449873358a8703b9c5a5809c57

desktop/flipper-ui-browser/src/initializeRenderHost.tsx

@@ -70,6 +70,10 @@ export function initializeRenderHost(
       // eslint-disable-next-line no-eval
       return eval(source);
     },
+    getStaticResourceUrl(path): string {
+      // the 'static' folder is mounted as static middleware in Express at the root
+      return '/' + path;
+    },
   } as RenderHost;
 }