Warn when a user defined error message references undefined names

Currently dotty doesn’t warn when you reference an unknown type parameter, but silently accepts it. It might be friendlier towards the user to warn that he probably made a typo.

scala> @annotation.implicitNotFound("Bar[${B}] not found") trait Bar[A] 
// defined trait Bar
scala> implicitly[Bar[String]] 
1 |implicitly[Bar[String]]
  |                       ^
  |                       Bar[${B}] not found

[YourPsychiatrist]

Just for the reference, I want to also add the def case to this issue since its in the same domain:

class K[A] {
  def m[B](implicit c: C[List[A], B]) = 0
  def n[B](implicit @implicitNotFound("Specific message for C of list of ${A} and ${B}") c: C[List[A], B]) = 1
}

For the sake of completeness, I feel like this issue should also cover this case (more generally, for all DefDefs, including constructors)

[YourPsychiatrist]

Ah! Thank you kindly, then I should be all set.