layout.js: Ignore actors without a metawindow in

isPopupMetaWindow().

Popups from layer-shell clients can end up triggering this. We may
want to eventually identify them but for now ignore, as any layer-
shell-based actor will be above or below the window stack anyhow.

cinnamonEntry.js: Allow addContextMenu() to re-use an existing

PopupMenuManager.

If the St.Entry is inside of a popup menu (and *not* a modal dialog),
that menu's 'captured-event' handler can receive unintended events,
and react to focus loss, closing both the original popup and context
menu.

The original menu's manager can safely deal with multiple popups,
and ensure 'correct' behavior in this situation.

ref:
#13472

Silence some gir-2.0-related warnings.

Silence some gir-2.0-related warnings.