Tracking interactions

Summary:
Set up basic primitives for user interaction tracking. I hope the docs and unit tests in this diff are self explanatory :)

In upcoming diffs:
* Wire up to scuba events
* Annotate all important parts of Flipper Chrome
* Investigate if we can wrap important interactions of ANT by default

Reviewed By: jknoxville

Differential Revision: D25120234

fbshipit-source-id: 9849d565d7be27e498cc2b4db33e7d6e6938ee06

desktop/flipper-plugin/src/index.ts

@@ -52,6 +52,14 @@ export {
 } from './ui/NUX';
 
 export {renderReactRoot} from './utils/renderReactRoot';
+export {
+  Tracked,
+  TrackingScope,
+  setGlobalInteractionReporter as _setGlobalInteractionReporter,
+  withTrackingScope,
+} from './ui/Tracked';
+
+export {sleep} from './utils/sleep';
 
 // It's not ideal that this exists in flipper-plugin sources directly,
 // but is the least pain for plugin authors.