Allow wiki macros to change their parameters during their execution

This issue is in the same scope as XWIKI-18063 ; when being displayed, a wiki macro could be able to change its own parameters in the document in which it is used.

While this feature may look strange at first glance, it can actually be very interesting if we consider the case of documents being edited through WYSIWYG : when starting to edit a document in WYSIWYG, XWiki will render the document in HTML (and thus, will execute the macros of the document). A macro can then wait for its execution in such context, and pre-load its parameters with some defaults. Then, through the wikimacroparameter macro, this pre-loaded content becomes editable in WYSIWYG mode transparently for the user