Allow Element Call to send call notifications

For clients which integrate Element Call: Currently matrix-rust-sdk is responsible for sending the call notification event when joining MatrixRTC sessions, but this is planned to be changed soon. As of the upcoming Element Call 0.14.0 release, it will request the capability to send call notifications itself, and we should auto-approve this capability.

bindings/matrix-sdk-ffi/src/widget.rs

@@ -197,6 +197,15 @@ pub fn get_element_call_required_permissions(
         .chain(read_send.clone())
         .collect(),
         send: vec![
+            // To notify other users that a call has started.
+            WidgetEventFilter::MessageLikeWithType {
+                event_type: "org.matrix.msc4075.rtc.notification".to_owned(),
+            },
+            // Also for call notifications, except this is the deprecated fallback type which
+            // Element Call still sends.
+            WidgetEventFilter::MessageLikeWithType {
+                event_type: MessageLikeEventType::CallNotify.to_string(),
+            },
             // To send the call participation state event (main MatrixRTC event).
             // This is required for legacy state events (using only one event for all devices with
             // a membership array). TODO: remove once legacy call member events are