Include the ancestor field ast in the resolver's `ResolveInfo`

Just as how `field_asts` contains the descendants to be resolved after a resolver, it would be nice if the `ResolveInfo` object also contains the field ast's ancestors that leads to the currently-resolved field.

This information would make https://github.com/graphql-python/graphql-core/issues/127 really easy to resolve.

Start by tracing the ResolveInfo definition and the existing field_asts population through the resolver path. Add access to the current field's ancestor ASTs, then verify that ResolveInfo exposes the expected ancestor chain and that the related issue 127 use case can obtain it.

Vom Indexierungsmodell aus dem Issue-Text verfasst.