SHACL - Backwards-chaining RDFS connection should use statistics

[hmottestad]

The backwards-chaining RDFS connection in the ShaclSail uses a fixed (10) size for deciding when to call hasStatement with each inferred type or calling getStatement and checking against each inferred type instead.

We should use statistics to determine the expected size of the getStatements call to compare with the number of inferred types in order to determine what to do.

Statistics is however not available at this level (wrapped connection).