typeahead: Fix bug where typeahead showed momentarily on shift + tab.

Since the keyup event for keys including shift triggers the typeahead,
shift tabbing into the topic recipient field would show the typeahead
momentarily, which is distracting.

As we need typeahead to trigger on shift for certain use cases in the
compose box, but not in the topic recipient field, we now do not trigger
typeahead on shift keyup events in the topic recipient field.

Fixes: #24152.

web/third/bootstrap-typeahead/typeahead.js

@@ -526,6 +526,13 @@ import {get_string_diff} from "../../src/util";
           }
           break
 
+        // to stop typeahead from showing up momentarily
+        // when shift + tabbing to the topic field
+        case 16: // shift
+          if (e.currentTarget.id === "stream_message_recipient_topic") {
+            return;
+          }
+
         default:
           var hideOnEmpty = false
           // backspace