Resolve grouping type eagerly in PropertyStatistics constructor

The fd5828f refactoring introduced lazy grouping type detection via
_resolve_type(), but only wired it into get_grouping_information().

The /queries endpoint calls get_query_for_items_for_property_positive()
without ever calling get_grouping_information(), so grouping_type
remained None, causing an AttributeError on the line_type property.

Before fd5828f, this was not an issue: bare properties (e.g. P175)
were resolved eagerly via the pywikibot API in GroupingConfigurationMaker,
and predicate paths (e.g. P131/P131) used PredicateGroupingConfiguration
which defaulted to ItemGroupingType() when grouping_type was None.

Her we move _resolve_type() into PropertyStatistics.init so it runs once
at construction time, regardless of which code path is taken afterwards.
Remove the now-redundant call from get_grouping_information().