[RN] add support for inviting participants during a call on mobile

* Button conditionally shown based on if the feature is enabled and available
* Hooks for launching the invite UI (delegates to the native layer)
* Hooks for using the search and dial out checks from the native layer (calls back into JS)
* Hooks for handling sending invites and passing any failures back to the native layer
* Android and iOS handling for those hooks

Author: Ryan Peck <rpeck@atlassian.com>
Author: Eric Brynsvold <ebrynsvold@atlassian.com>

react/features/app/components/App.native.js

@@ -37,6 +37,10 @@ export class App extends AbstractApp {
     static propTypes = {
         ...AbstractApp.propTypes,
 
+        addPeopleEnabled: PropTypes.bool,
+
+        dialOutEnabled: PropTypes.bool,
+
         /**
          * Whether Picture-in-Picture is enabled. If {@code true}, a toolbar
          * button is rendered in the {@link Conference} view to afford entering