Remove a resolver's query splitting when the projection loads no collection

[SimonCropp]

A resolver can call AsSplitQuery() for the collections a request might select. When the request selects none, the select projection loads no collection, so the split does nothing. Verify.EntityFramework 16 throws for that:

AsSplitQuery() is ignored, since the query loads no collection.

For example, a connection field whose resolver is Commitments.AsSplitQuery()... failed for any request that selected only scalars.

ApplyProjection now checks whether the projection loads a collection at any depth, including derived-type navigations. If it doesn't, AsSplitQuery() and AsSingleQuery() are removed from the query (new QuerySplitting). The query is left alone when a collection is selected, and when projection falls back to includes, since a collection can then come from a resolver Include or an AutoInclude.

Tests: a splitParentEntitiesConnection field whose resolver calls AsSplitQuery().

• Selecting only scalars used to throw. It now runs one page query.
• Selecting children still splits them into a second query.