We report bitmaps as being 'on' a copper layer because they are
associated with it but they are not actually physical parts so should
not be included in the DRC checks
Additionally, Bitmaps effective shape starts are the top left corner
rather than the center (unclear why that was there in the first place)
Fixes https://gitlab.com/kicad/code/kicad/issues/14065
(cherry picked from commit 1b8b216ac8)
Also adds some debugging to try to catch dangling pointers.
Also adds a cache for group bounding boxes (which will be expensive
to calculate for large groups).
Fixes https://gitlab.com/kicad/code/kicad/issues/12875
Seth Hillbrand
Jon Evans
Jeff Young
Mike Williams
Marek Roszko
jean-pierre charras