api: Add read_by_sender flag to sendMessage

This flag allows the client to communicate to the
server that the new message should be initially
marked as read for its sender.
Added in FL 236 in zulip/zulip#28204 .

Fixes: zulip#440

lib/api/route/messages.dart

@@ -179,6 +179,7 @@ Future<SendMessageResult> sendMessage(
   String? localId,
 }) {
   final supportsTypeDirect = connection.zulipFeatureLevel! >= 174; // TODO(server-7)
+  final supportsReadBySender = connection.zulipFeatureLevel! >= 236; // TODO(server-8)
   return connection.post('sendMessage', SendMessageResult.fromJson, 'messages', {
     if (destination is StreamDestination) ...{
       'type': RawParameter('stream'),
@@ -193,6 +194,7 @@ Future<SendMessageResult> sendMessage(
     'content': RawParameter(content),
     if (queueId != null) 'queue_id': queueId,
     if (localId != null) 'local_id': localId,
+    if (supportsReadBySender) 'read_by_sender': 'true',
   });
 }
 

test/api/route/messages_test.dart

@@ -314,6 +314,20 @@ void main() {
 
     test('to stream', () {
       return FakeApiConnection.with_((connection) async {
+        await checkSendMessage(connection,
+          destination: StreamDestination(streamId, topic), content: content,
+          expectedBodyFields: {
+            'type': 'stream',
+            'to': streamId.toString(),
+            'topic': topic,
+            'content': content,
+            'read_by_sender': 'true',
+          });
+      });
+    });
+
+    test('to server without read_by_sender support', () {
+      return FakeApiConnection.with_(zulipFeatureLevel: 235, (connection) async {
         await checkSendMessage(connection,
           destination: StreamDestination(streamId, topic), content: content,
           expectedBodyFields: {