migrated AggregateExplainOperation tests.
ported AggregateOPeration tests to Core.
ported AggregateToCollectionOperation tests.
removed function count operation tests.
ported DatabaseExistsOperations tests.
ported DistinctOperation tests.
ported ListCollectionNamesOperation tests.
ported FindOneAndDeleteOperation tests.
ported FindOneAndReplaceOperation tests.
ported FindOneAndUpdateOperationt tests.
ported FindOperation tests and beefed up related tests.
ported ExplainOperation tests.
ported InsertOpcodeOperation tests.
porting BulkMixedWriteOperation tests.
removed Core.FunctionalTests assembly.
formatted files and removed using statements.
CR Changes.