sequel for #90 covered with test
original PR is been inactive for half a year, I decided to open a new one

Original description:

What

Update QueryComplexity.ts to count meta fields against total complexity. The current implementation only considers fields included in the schema, which omits: __typename, __type and __schema.

Why

Denial of service attacks are possible by creating many aliases of meta fields:

query LargeQuery {
 __typename
 alias1: __typename
 alias2: __typename
 ...
 alias1000: __typename
}

edit:
simple 300kb with 35k __typename fields query is able to load server for almost half-a-minute. It can be used for DoS attacks.

Considerations

If counting each field as 1 cost, common introspection queries will have a cost around 180. Consumers of the library may need to increase the maximum.

edit: Probably, to keep compatibility, we can make some optional parameter to include these fields in total complexity, but I think it's unnecessary