XWikiDocument#display should check if we are inside an html macro

XWikiDocument#display always wraps the output in an html macro if the displayer produces html. The problem is that it does not check if we are already inside an html macro, which might lead to bad pattern such as closing an html macro before calling display() or even, stripping the html macro wrapping after the call.

The method should probably checks if we're already inside an html macro to avoid this wrapping in such case.
See an example of such usage: https://github.com/xwiki/xwiki-platform/pull/1733#discussion_r774453667