Classes do not correctly list all interfaces they implement

[Chriscbr]

The AWS CDK documentation shows the interfaces that are implemented by a given class:

This is mirrored in jsii-docgen, except the information doesn't always match. For example on Construct Hub (which uses jsii-docgen under the hood), the page for CfnAccessPoint says that it only implements IInspectable (at the time of creating this issue) -- but the AWS CDK API Reference shows that it implements IInspectable, IConstruct, and IDependable.

My hunch is that there is a bug in how we're obtaining the list of interfaces -- perhaps the code is omitting interfaces implemented by superclasses, or omitting interfaces that are extended by other interfaces, etc.