When a hierarchical bus connects sheets, local labels that are bus members
may only connect to pins through the hierarchy (in other sheets). Previously,
ERC counted pins from all sheets connected through the hierarchy, which masked
labels that lacked local connections.
Now, for local labels that are bus members, we track local pin count separately.
If a bus member label has no local pin connections, it is flagged as unconnected
even if the net has pins in other sheets through the hierarchical bus.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/19646
Seth Hillbrand
c5840cacdb