Allow impls and traits having static and instance methods with the same name

[ttaubert]

This fixes all errors described in issue #4265. make check runs successfully on my machine.

r? @brson

[catamorphism]

I reviewed since I suspect not too many other core team members are working on Christmas Eve ;-) Looks good except for my line comment -- if you can fix that and re-push, I'll merge it. Thanks!

[brson]

Do we have agreement that this is a desirable feature? Actually defining two methods with the same name seems like something you would never want to do.

[catamorphism]

@brson I thought about that, but is there a specific reason we'd want to rule it out? Is there a scenario where allowing two methods with the same name could confuse somebody?

[brson]

@catamorphism Besides making it more difficult to talk about that method with the duplicate name, I don't have any specific problems with it.

This is probably incompatible with @pcwalton's proposal to unify methods and functions.

[ttaubert]

@catamorphism Thank you for the quick review!

@brson I agree that this might not be what we want but I figured since we support defining those methods we should also support calling them. OTOH if this really interferes with @pcwalton's proposal (which I think is really nice) we should just fail when we encounter a taken method name.

[pcwalton]

I think this interferes incompatibly with my proposal.

[brson]

Closing because this prevents the unification of methods and functions per @pcwalton's proposal. Can we fix this issue instead by emitting an error when static and instance methods have the same name?