Support free text search

I continue to hear from potential Artificer users that support "free text search", where both metadata and artifact content are considered, is vital. And I agree, especially when considering the emphasis on artifact discovery and re-use.

I'd argue that 'xp2:matches' be extended to support artifact content, as well as metadata. For instance, xp2:matches(., 'foo') would search for any artifact containing "foo" in its metadata or content. A specific value could be created to specifically search content on its own – something like xp2:matches(@content, 'foo')