Upgrading to dgeni-packages 0.21.4 gives us
access to more properties on the API docs, which
allows us to fix the following issues:
Closes#19450Closes#19452Closes#19456
For classes, the tree of subclasses is rendered, recursively.
For interfaces, the descendants are separated into child interfaces, which
extend the interface, and classes, which implement the interface.
Closes#19306