Issue a warning when an implicit view is resolved in `-source:3.0-migration`

[adpi2]

Minimized example

trait Pretty {
  val print: String
}

object Pretty {
  def pretty[A](a: A)(implicit ev: A => Pretty): String = a.print
}

Output

The above code compiles with -source:3.0-migration but it does not issue a warning. This is an issue because in some cases the code compiles in both migration and standard modes but the runtime behavior is not the same. See below example:

trait Pretty {
  val print: String
}

object Pretty {
  implicit def prettyAny(any: Any): Pretty = new Pretty { val print = "" }
  def pretty[A](a: A)(implicit ev: A => Pretty): String = a.print
}

Expectation

In the migration mode, when an implicit view is resolved a warning should be issued.
The -language:implicitConversions option should not mute this warning.