1) Don't wait for UpdateUserInterface to build the (global) list of
layer names.
2) Report clearance resolution between a silk layer and a mask layer.
3) When writing DRC reports, include info about the violating rule.
4) Report "no relevant layers" if we fail to find anything to write
a clearance resolution report about.
Fixes https://gitlab.com/kicad/code/kicad/issues/8963