Enable implemented class to call implemented procedures in `protocol`

[glassesneo]

protocol SomeProtocol:
  proc implemented(x: int) =
    return x

class SomeClass impl SomeProtocol:
  discard

let some = SomeClass.new()

some.implemented(5)

[glassesneo]

• how to resolve the conflict between a protocol that has implemented procs and one that doesn't
• whether a class can override implemented procs