Enable e2ee support (#274)

* Enable sliding sync common extensions and session verification banner display; fix user session flow coordinator state machine
* Fixed a couple of deprecation warnings
* Add missing `m.room.encryption` required state
* Switch to rust-sdk v1.0.15-alpha and add changelog

UITests/Sources/Application.swift

@@ -63,11 +63,11 @@ extension XCUIApplication {
     }
 
     private var languageCode: String {
-        Locale.current.languageCode ?? ""
+        Locale.current.language.languageCode?.identifier ?? ""
     }
 
     private var regionCode: String {
-        Locale.current.regionCode ?? ""
+        Locale.current.language.region?.identifier ?? ""
     }
 
     private var osVersion: String {