Add support for sharing URLs and text. (#3546)

* Add support for sharing URLs and text.

* Fix a bug where a stored draft would overwrite the shared text.

* Add tests.

ElementX/Sources/Mocks/JoinedRoomProxyMock.swift

@@ -123,6 +123,7 @@ extension JoinedRoomProxyMock {
         matrixToEventPermalinkReturnValue = .success(.homeDirectory)
         loadDraftReturnValue = .success(nil)
         clearDraftReturnValue = .success(())
+        sendTypingNotificationIsTypingReturnValue = .success(())
     }
 }