Call graph: only show source location paths for external callers/callees

[weinand]

testing #71083:

In your sample all callers and callees are located in a single source file. In this case it is very noisy to duplicate the same source path for each node in the call graph:

I suggest to only show paths for nodes that are outside of the current source file. So in the sample no path would show up.

In a more realistic scenario I could easily see with this approach what part of the call hierarchy is local in the source file and what is external.

[jrieken]

The path is actually just a fallback. The api defines CallHierarchyItem#detail and when that's missing it falls back to the filename. The idea is that detail is something like the signature of fully qualified name.

I would just nuke that fallback, showing the symbol name without the filename then.