[ShadowDOM] Implement moveBefore()

## Description

`moveBefore()` is a new API similar to `insertBefore()`. I won't be possible to polyfill, but ShadyDOM could possibly wrap it when available to create the right DOM structure.

A good addition here would be to only patch `moveBefore()` when it's available natively so that feature detection in library code still works.

## Motivation

When working on `moveBefore()` support for lit-html, I hit an error with the polyfill tests: https://github.com/lit/lit/pull/4838

I haven't made a minimal reproduction yet, but the native function is complaining about an invalid hierarchy.