pkg/lib: fix context menu component popdown

f9b0166 changed the popdown behaviour of the context menu.

Before that commit, the previous code was wrong.  It was:

     const wasOutside = !(event.target.contains === root.current);

     if (wasOutside)
         setVisible(false);

but because `event.target.contains` is a function, the comparison was
always false and wasOutside would always be true.  This meant that any
left click would always pop the menu down.

The replacement code was:

    const wasOutside = !event.target.contains(root.current);

which at least looks like it does something meaningful.  Unfortunately
this is also wrong, but in the other direction: this means that the menu
will only pop down if it's not contained inside of the item you've
clicked on.  If you click on a large top-level <div> (ie: something
which effectively contains "most things") then the menu will remain
shown.  That's definitely wrong.

We seemed to be happy with the behaviour before the original change, but
the code has a purpose: it allows clicking on content of the menu (like
on a divider, for example) without dismissing it.  Let's try to
implement the intended original behaviour: we should dismiss the menu
only if the element that we clicked on is outside of the menu:

    const wasOutside = root.current && !root.current.contains(event.target);

Fixes #20649

pkg/lib/cockpit-components-context-menu.tsx

@@ -48,7 +48,7 @@ export const ContextMenu = ({ parentId, children } : {
 
         const _handleClick = (event: MouseEvent) => {
             if (event && event.button === 0 && event.target instanceof HTMLElement) {
-                const wasOutside = !event.target.contains(root.current);
+                const wasOutside = root.current && !root.current.contains(event.target);
 
                 if (wasOutside)
                     setVisible(false);