Add action to user detail dialog to search for their messages in room

In other messaging applications (e.g. Discord) this is possible through
text modifiers like "from:@user". We don't support that, and I'm not
super keen on implementing yet-another-parsing-thing, so an action in
the user detail dialog should work for now.

Very useful to sift through large rooms but when you only care about a
specific person's messages (maybe your own?)

src/app/qml/UserDetailDialog.qml

@@ -274,6 +274,20 @@ Kirigami.Dialog {
             }
         }
 
+        FormCard.FormButtonDelegate {
+            text: i18nc("@action:button %1 is the name of the user.", "Search room for %1's messages", root.room ? root.room.member(root.user.id).htmlSafeDisplayName : QmlUtils.escapeString(root.user.displayName))
+            icon.name: "search-symbolic"
+            onClicked: {
+                pageStack.pushDialogLayer(Qt.createComponent('org.kde.neochat', 'RoomSearchPage'), {
+                    room: root.room,
+                    senderId: root.user.id
+                }, {
+                    title: i18nc("@action:title", "Search")
+                });
+                root.close();
+            }
+        }
+
         FormCard.FormButtonDelegate {
             text: i18n("Copy link")
             icon.name: "username-copy"