Element Call ringing notifications (#2978)

- Add `ActiveCallManager` to handle incoming and ongoing calls.
- Add ringing call notifications with full screen intents and missed call ones as part of the 'conversation' notifications.

---------

Co-authored-by: ElementBot <benoitm+elementbot@element.io>

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/room/MatrixRoom.kt

@@ -332,5 +332,10 @@ interface MatrixRoom : Closeable {
      */
     suspend fun getPermalinkFor(eventId: EventId): Result<String>
 
+    /**
+     * Send an Element Call started notification if needed.
+     */
+    suspend fun sendCallNotificationIfNeeded(): Result<Unit>
+
     override fun close() = destroy()
 }

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/timeline/item/event/EventType.kt

@@ -72,6 +72,7 @@ object EventType {
     const val CALL_NEGOTIATE = "m.call.negotiate"
     const val CALL_REJECT = "m.call.reject"
     const val CALL_HANGUP = "m.call.hangup"
+    const val CALL_NOTIFY = "m.call.notify"
 
     // This type is not processed by the client, just sent to the server
     const val CALL_REPLACES = "m.call.replaces"
@@ -94,6 +95,7 @@ object EventType {
             type == CALL_SELECT_ANSWER ||
             type == CALL_NEGOTIATE ||
             type == CALL_REJECT ||
-            type == CALL_REPLACES
+            type == CALL_REPLACES ||
+            type == CALL_NOTIFY
     }
 }