cmd/doc, go/doc: add basic support for generic code
Update cmd/doc and go/doc for the generics, by adding handling for type
parameters and the new embedded interface elements.
Specifically:
- Format type parameters when summarizing type and function nodes.
- Find the origin type name for instantiation expressions, so that
methods are associated with generic type declarations.
- Generalize the handling of embedding 'error' in interfaces to
arbitrary predeclared types.
- Keep embedded type literals.
- Update filtering to descend into embedded type literals.
Also add "any" to the list of predeclared types.
Updates #49210
Change-Id: I6ea82869f19c3cdbc3c842f01581c8fc7e1c2ee7
Reviewed-on: https://go-review.googlesource.com/c/go/+/359778
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>