R1:a44de4f76c4e

Link interfaces as classes

Summary:
We link classes from `extends` and `instanceof` (which can be both interface and class) and from `implements` (which is always interface).

We don't need to split these two because they share the same namespace.
If we decide to then we will need to:

- Fix [[ https://secure.phabricator.com/diffusion/P/browse/master/src/applications/diffusion/controller/DiffusionSymbolController.php;66a300768a62bbc9$79 | DiffusionSymbolController ]]
- Fix [[ https://secure.phabricator.