fix: Prosemirror inside Webcomponent needs to use ownerDocument

[serranoio]

When Prosemirror is initialized inside a webcomponent, this.prosemirrorView._root is a ShadowRoot which does not have acreateRange method available on it, causing this error.

• This is backwards compatible:
  If createRange function is available, _root is Document, so no change
  if not, _root we assume it is ShadowRoot, and use the .ownerDocument function.

• the code does not error on getSelection, but for consistency, I made the change here too 👍

Lmk if you have any questions :). I'd be happy to repro as well

[serranoio]

Just saw #193. This is the same issue. However, this solution is backwards compatible