Move the "Show User" action to DelegateContextMenu, add it for media

This was missing from the media context menu, and should be added. Since
it's shared between messages and files, it's now a common action.

src/qml/MessageDelegateContextMenu.qml

@@ -66,13 +66,7 @@ DelegateContextMenu {
             onTriggered: Clipboard.saveText(root.selectedText.length > 0 ? root.selectedText : root.plainText)
         },
         DelegateContextMenu.ReportMessageAction {},
-        Kirigami.Action {
-            text: i18nc("@action:inmenu", "Show User")
-            icon.name: "username-copy"
-            onTriggered: {
-                RoomManager.resolveResource(author.id)
-            }
-        },
+        DelegateContextMenu.ShowUserAction {},
         DelegateContextMenu.ViewSourceAction {},
         Kirigami.Action {
             text: i18n("Copy Link")