Determine Which Theme Files are Actually in Use

Is there a fancy (or mundane) function that will show which theme files are actually in use vs those that came along for the ride in previous upgrades?

I've got a number of Widget-{widget name} files that I think came along from v10 to v11 and are now not flagged as changed in v12 but are flagged as new in comparison to factory defaults. I think I can probably delete them, but looking for a gut check on if they're actually being called/relied upon by a widget.