If the feature is enabled, allow method `self` types to be any type
that auto-derefs to `self`.
- Currently, this supports inherent methods as well as trait methods.
The plan AFAIK is to only allow this for trait methods, so I guess it
won’t stay this way
- Dynamic dispatch isn’t implemented yet, so the compiler will ICE if
you define a trait method that takes `self: Rc<Self>` and try to call
it on an `Rc<Trait>`. I will probably just make those methods
non-object-safe initially.
497397ab4b