FORM elements processing can fail in browser environment with INPUT fields shadowing node properties

[pavelhoral]

The gist of the issue - https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement#issues_with_naming_elements

Due to a problematic HTMLFormElement behavior the child input elements can shadow Node properties that are being used by Turndown. For example the following will break Turndown parsing:

<form><input id=parentNode>

Credits to ixSly for reporting this issue.

[pavelhoral]

Few additional notes:

• This issue is only present in browser based DOM implementation. Domino parsing is unaffected.
• Any node property can get shadowed by this (firstChild, nextSibling, parentNode, childNodes, ...)

Fixing this might require some sort of wrapping to actually get "clean" Node behavior (thinking of something similar to Vue's reactive()).