Explicitly state Firestore's dependency on UIKit (#5067)
Explicitly state Firestore's dependency on UIKit (#5067)

In #4985 we added support for listening to
`UIApplicationWillEnterForegroundNotification` notifications to better
handle situations where we may have missed callbacks from
`SCNetworkReachabilitySetCallback` while Firestore was in the background.

Fixes #5065.
firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk