Add support for fourfold nested lists in introspection

[gschulze]

This PR adds support for introspecting four-fold nested lists, which in turn allows proper representation of GeoJSON multipolygons (https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.7).

Closes #2643

[linux-foundation-easycla]

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• ✅ login: gschulze / name: Gunnar Schulze (28e4ea5)

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[IvanGoncharov]

@gschulze Thank you for explaining why you need this.
Definitely worth merging, if you need it in the v16 line please submit a PR to the 16.x.x branch.

P.S. We definitely need to add something to the spec to properly solve this problem 🤔

[gschulze]

@IvanGoncharov thanks for merging! I made a PR to the 16.x.x branch as you proposed: #3950

I think the underlying problem more or less boils down to always having to specify every field at every level. Maybe having wildcard support like proposed in graphql/graphql-spec#127 would help here. That also would make handling of polymorphic types much easier on the client side.