Add FileSelector shared component

Summary: Add shared FileSelector component compatibe with the new FlipperLib API

Reviewed By: mweststrate

Differential Revision: D32667100

fbshipit-source-id: dca1e8b7693d134a99617e916c7cfd30432cef78

desktop/flipper-plugin/src/__tests__/api.node.tsx

@@ -38,6 +38,7 @@ test('Correct top level API exposed', () => {
       "DetailSidebar",
       "Dialog",
       "ElementsInspector",
+      "FileSelector",
       "Layout",
       "MarkerTimeline",
       "MasterDetail",