Include meta fields (__typename, __type, __schema) against total field complexity

[jvanst]

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
}

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.

[ivome]

@jvanst Good catch! Thanks for the PR. Would you mind adding some tests for this?

[Squarix]

@ivome @jvanst very important changes, any news on this pr?

[ivome]

Obsolete with #92 merged