message_ui: Prevent action buttons from hiding on recipient bar focus.

Added `visibility` CSS with `:focus-within` pseudo-class to
the recipient bar. This keeps the action button visibility
consistent with the action UIs - topic editing UI and notification
menu.

Fixes part of #26852.

Co-authored by: ecxtacy <dc.dhruvchouhan@gmail.com>

web/styles/message_header.css

@@ -80,6 +80,11 @@
             visibility: hidden;
         }
 
+        /* When any of the actions are focused, don't hide them */
+        .recipient_bar_controls:focus-within {
+            visibility: visible;
+        }
+
         /* Show the bar controls on hover and when the bar is sticky */
         &:hover {
             .recipient_bar_controls {

web/styles/zulip.css

@@ -901,6 +901,7 @@ div.focused-message-list.is-conversation-view .recipient_row {
 .topic_edit {
     display: none;
     line-height: 22px;
+    visibility: visible;
 
     .alert {
         display: inline-block;