Implement SPARQL query engine dependency injection

Both PropertyStatistics and GroupingConfiguration make
SPARQL queries, using the pywikibot.data.sparql module.

Here we wrap the calls to pywikibot's module
(and thus the call to the SPARQL engine)
as the WdqsSparqlQueryEngine class.

The object can be injected into PropertyStatistics,
and it is also passed to get_grouping_information.

This requires quite a few changes to the PropertyStatistics unit tests.

This paves the way to use alternative SPARQL query engines (T385749).

Bug: T385749