compose [nfc]: Abstract out ComposeTopicController.setTopic

Author: gnprice

lib/widgets/action_sheet.dart

@@ -645,7 +645,7 @@ class QuoteAndReplyButton extends MessageActionSheetMenuItemButton {
       && composeBoxController.topic.textNormalized == kNoTopicTopic
       && message is StreamMessage
     ) {
-      composeBoxController.topic.value = TextEditingValue(text: message.topic);
+      composeBoxController.topic.setTopic(message.topic);
     }
 
     // This inserts a "[Quoting…]" placeholder into the content input,

lib/widgets/autocomplete.dart

@@ -322,7 +322,7 @@ class TopicAutocomplete extends AutocompleteField<TopicAutocompleteQuery, TopicA
     final intent = autocompleteIntent();
     if (intent == null) return;
     assert(intent.syntaxStart == 0);
-    controller.value = TextEditingValue(text: option.topic);
+    controller.setTopic(option.topic);
     contentFocusNode.requestFocus();
   }
 

lib/widgets/compose_box.dart

@@ -89,6 +89,10 @@ class ComposeTopicController extends ComposeController<TopicValidationError> {
         TopicValidationError.tooLong,
     ];
   }
+
+  void setTopic(String newTopic) {
+    value = TextEditingValue(text: newTopic);
+  }
 }
 
 enum ContentValidationError {