Extension method Query<T> doesn't support entity names

The new LinQ infrastructure doesn't support entity names. To add support an overload similar to the one of the old LinQ provider would be needed.

I attached a patch I used to add support for entity names to the new LinQ provider. It works as expected.

IMPORTANT: It is necessary to override ToString() because the query plans are different for each entity and the ToString representation is used within the query cache otherwise the cache only store one plan per entity type.