lean harder on source locations as provenance in tooling

[cscheid]

Now that we can have metadata merging in Quarto Hub, it would be amazing to show in tooling where author data comes from, etc.

[cscheid]

From @vezwork:

[cscheid]

Another thing we realized we can do - we can traverse the source location structure in the document to find out a list of documents we depend on (so changes on those documents should trigger a rerender). That list is not perfect, but is much better than just watching the .qmd itself.