Show ellipses for leaving rooms and space actions, and always confirm

The HIG suggests using ellipses for actions that have a confirmation,
and leaving a space or room is one such cases. Otherwise, the user has
no idea if leaving is an immediate, irreversible action.

It turns out there *was* some cases where pressing this button
(especially for spaces) would actually do it without confirmation, which
is now fixed.

src/rooms/RoomContextMenu.qml

@@ -152,7 +152,7 @@ KirigamiComponents.ConvergentContextMenu {
     }
 
     QQC2.Action {
-        text: i18n("Leave Room")
+        text: i18n("Leave Room…")
         icon.name: "go-previous"
         onTriggered: {
             Qt.createComponent('org.kde.neochat', 'ConfirmLeaveDialog').createObject(root.QQC2.ApplicationWindow.window, {