Fix: Voice Messages don't restore audio to speaker when held up to the ear past

the voice notes duration.

Specifically:

- start a voice note
- hold to ear until complete
- remove from ear
- start another voice note (or the same one) with the phone away from your ear

You'd expect audio to play through the external speaker, but instead it comes
through the earpiece.

Based on the added logging, this seems to be an apple bug.

SignalMessaging/utils/ProximityMonitoringManager.swift

@@ -13,6 +13,16 @@ public class OWSProximityMonitoringManagerImpl: NSObject, OWSProximityMonitoring
     var lifetimes: [Weak<AnyObject>] = []
     let serialQueue = DispatchQueue(label: "ProximityMonitoringManagerImpl")
 
+    public override init() {
+        super.init()
+
+        // TODO: change to `runNowOrWhenAppWillBecomeReady` when
+        // reverse integrating
+        AppReadiness.runNowOrWhenAppIsReady {
+            self.setup()
+        }
+    }
+
     // MARK: 
 
     var device: UIDevice {
@@ -39,20 +49,44 @@ public class OWSProximityMonitoringManagerImpl: NSObject, OWSProximityMonitoring
         }
     }
 
+    @objc
+    public func setup() {
+        NotificationCenter.default.addObserver(self, selector: #selector(proximitySensorStateDidChange(notification:)), name: .UIDeviceProximityStateDidChange, object: nil)
+    }
+
+    @objc
+    func proximitySensorStateDidChange(notification: Notification) {
+        Logger.debug("")
+        // This is crazy, but if we disable `device.isProximityMonitoringEnabled` while
+        // `device.proximityState` is true (while the device is held to the ear)
+        // then `device.proximityState` remains true, even after we bring the phone
+        // away from the ear and re-enable monitoring.
+        //
+        // To resolve this, we wait to disable proximity monitoring until `proximityState`
+        // is false.
+        if self.device.proximityState {
+            self.add(lifetime: self)
+        } else {
+            self.remove(lifetime: self)
+        }
+    }
+
     func reconcile() {
         if _isDebugAssertConfiguration() {
             assertOnQueue(serialQueue)
         }
         lifetimes = lifetimes.filter { $0.value != nil }
         if lifetimes.isEmpty {
-            Logger.debug("disabling proximity monitoring")
             DispatchQueue.main.async {
+                Logger.debug("disabling proximity monitoring")
                 self.device.isProximityMonitoringEnabled = false
             }
         } else {
-            Logger.debug("enabling proximity monitoring for lifetimes: \(lifetimes)")
+            let lifetimes = self.lifetimes
             DispatchQueue.main.async {
+                Logger.debug("willEnable proximity monitoring for lifetimes: \(lifetimes), proximityState: \(self.device.proximityState)")
                 self.device.isProximityMonitoringEnabled = true
+                Logger.debug("didEnable proximity monitoring for lifetimes: \(lifetimes), proximityState: \(self.device.proximityState)")
             }
         }
     }