internal: Add ApiNarrowIsMentioned.

Maybe we can try to generalize these "ApiNarrowIs"s classes when we
support more "is:" operands.

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/api/model/narrow.dart

@@ -115,6 +115,13 @@ class ApiNarrowPmWith extends ApiNarrowDm {
 }
 
 // TODO: generalize into ApiNarrowIs
+class ApiNarrowIsMentioned extends ApiNarrowElement {
+  @override String get operator => 'is';
+  @override String get operand => 'mentioned';
+
+  ApiNarrowIsMentioned({super.negated});
+}
+
 class ApiNarrowIsUnread extends ApiNarrowElement {
   @override String get operator => 'is';
   @override String get operand => 'unread';

lib/model/internal_link.dart

@@ -85,6 +85,8 @@ Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
         fragment.write('${element.operand.join(',')}-$suffix');
       case ApiNarrowDm():
         assert(false, 'ApiNarrowDm should have been resolved');
+      case ApiNarrowIsMentioned():
+        fragment.write(element.operand.toString());
       case ApiNarrowIsUnread():
         fragment.write(element.operand.toString());
       case ApiNarrowMessageId():