Selector:Manipulation: Fix DOM manip within template contents

Selector:Manipulation: Fix DOM manip within template contents

The `<template/>` element `contents` property is a document fragment that may
have a `null` `documentElement`. In Safari 16 this happens in more cases due
to recent spec changes - in particular, even if that document fragment is
explicitly adopted into an outer document. We're testing both of those cases
now.

The crash used to happen in `jQuery.contains`. As it turns out, we don't need
to query the supposed container `documentElement` if it has the
`Node.DOCUMENT_NODE` (9) `nodeType`; we can call `.contains()` directly on
the `document`. That avoids the crash.

Fixes gh-5147
Closes gh-5158