Show page components referring to a document

Similar to existing "Show referring documents" option in "Document" menu, but instead listing page components referring to the document.

Also, warn when trying to delete a document which is being referred to from at least one page component (again, similar to the existing functionality for incoming links from other documents).

This is low-hanging fruit because it only takes a simple query to get all components where the document's relative path is a parameter value, e.g.

/jcr:root/hst:hst/hst:configurations/10/hst:workspace/hst:containers//element(*,hst:containeritemcomponent)[@hst:parametervalues='10/home/videobanner-hgt']

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Edit: after explanation from Ard I understand this is a more complex issue than it appears to be on the surface, and therefore can't be considered "low-hanging fruit". However we agreed that this functionality is a must-have on the way forward.

Note from PM: This needs design how the check will happen of what referenced documents are part of an experience page.