Add support for TypeORM's getRawAndEntities() method

I've hit a known limitation in TypeORM where it's not possible to select a computed value with an alias and then map it automatically to a property in my TypeORM entity. See this PR, as an example This can be worked around by the use of getRawAndEntities(), as demonstrated in this StackOverflow post. This method isn't supported through in the GraphQLQueryBuilder class, in the same way eg loadMany() maps through to getMany() for example. Is there any chance of adding this functionality?