feat(ios): adds ios screensharing enabled flag

ios/app/src/AppDelegate.m

 
     jitsiMeet.defaultConferenceOptions = [JitsiMeetConferenceOptions fromBuilder:^(JitsiMeetConferenceOptionsBuilder *builder) {
         [builder setFeatureFlag:@"resolution" withValue:@(360)];
+        [builder setFeatureFlag:@"ios.screensharing.enabled" withBoolean:YES];
         builder.serverURL = [NSURL URLWithString:@"https://meet.jit.si"];
         builder.welcomePageEnabled = YES;
 

react/features/base/flags/constants.js

  */
 export const IOS_RECORDING_ENABLED = 'ios.recording.enabled';
 
+/**
+ * Flag indicating if screen sharing should be enabled in iOS.
+ * Default: disabled (false).
+ */
+export const IOS_SCREENSHARING_ENABLED = 'ios.screensharing.enabled';
+
 /**
  * Flag indicating if kickout is enabled.
  * Default: enabled (true).

react/features/toolbox/components/native/ScreenSharingIosButton.js

 import { findNodeHandle, NativeModules, Platform } from 'react-native';
 import { ScreenCapturePickerView } from 'react-native-webrtc';
 
+import { getFeatureFlag, IOS_SCREENSHARING_ENABLED } from '../../../base/flags';
 import { translate } from '../../../base/i18n';
 import { IconShareDesktop } from '../../../base/icons';
 import { connect } from '../../../base/redux';
  * }}
  */
 function _mapStateToProps(state): Object {
+    const enabled = getFeatureFlag(state, IOS_SCREENSHARING_ENABLED, false);
+
     return {
         _screensharing: isLocalVideoTrackDesktop(state),
 
         // TODO: this should work on iOS 12 too, but our trick to show the picker doesn't work.
-        visible: Platform.OS === 'ios' && Platform.Version.split('.')[0] >= 14
+        visible: enabled && Platform.OS === 'ios' && Platform.Version.split('.')[0] >= 14
     };
 }