`ToplogyKernel::n_{vertices,...}()` includes deleted elements, counting logical elements would be useful
The n_* methods return the sizes of the underlying vectors, which can be different from the actual logical count when the mesh is not garbage collected.
I suggest we track the actual number of logical undeleted elements in counters, however returning those in n_* would be a breaking change, some code might rely on this behaviour.
My suggestion would be introducing n_logical_{vertices,...}() methods. Any thoughts (or better suggestions for a name), @moebius, @lyon?