Select2 inside ShadowRoot Broke In 4.0.11

#5584 breaks the usage of Select2 inside a ShadowRoot, because $.contains() returns false, even though the Node is actually connected to the document.

I’d propose changing the following code:

    if ($.contains(document.body, $offsetParent[0])) {
      parentOffset = $offsetParent.offset();
    }

To this:

    if ($offsetParent[0].isConnected) {
      parentOffset = $offsetParent.offset();
    }

[kevin-brown]

Probably going to switch this to

    if ($.contains(document.body, $offsetParent[0]) || $offsetParent[0].isConnected) {
      parentOffset = $offsetParent.offset();
    }

Just to handle IE/Edge/older browsers when they aren’t using the shadow DOM (because let’s be honest, they won’t be using the shadow DOM if they’re old enough to not support isConnected).

[lazka]

Since 4.0.11 (4.0.10 works) I also get wrong offsets for the popup:

This is also inside a Shadow DOM.