CSHARP-1075: Reimplement MongoDatabase CreateCollection using an operation in Core.
CSHARP-1075: Ported CreateCollectionOperationTests assertions from fluent NUnit assertions to FluentAssertions.
CSHARP-1075: Reimplement MongoDatabase DropCollection using operation in Core.
CSHARP-1075: Reimplement MongoServer DropDatabase using an operation in Core.
Made readPreference argument to ExecuteReadOperation optional with suitable defaults.
CSHARP-1075: Reimplement MongoServer GetDatabaseNames using an operation in Core.