Figure Block should be handled even when not inside a MacroMarkerBlock

This is a regression caused in the XWiki platform by XWIKI-16389 which changed the XDOM and removed MacroMarkerBlocks (MMB), see XWIKI-16708.

The reason it's causing problem in the LaTeX export is because we apply special handling for figure macros in the XDOM but since the MMBs are removed when a wikimacro is used, there's no longer the information that it's coming from a macro and thus the FigureBlock is just ignored.

This should normally be fixed by fixing XWIKI-16708 but I don't master how that works. Thus FTM, I'm going to implement a workaround and support handling of FigureBlock that are not inside a MMB.