Warn if @HasQualifierParameter is written on a supertype but not on a subtype

[mernst]

The manual says:

If a subclass extends a @HasQualifierParameter class (or implements a @HasQualifierParameter interface), then the subclass must also be marked @HasQualifierParameter.

It is difficult to diagnose the problem when @HasQualifierParameter is forgotten on a subtype.
Therefore, the Checker Framework should check for this condition, and issue a warning.

[smillst]

@HasQualifierParameter is marked @Inherited, so you shouldn't have to write it on a subtype. Do you have an example where this isn't working. Here's an example that produces errors because MyBuffer has a qualifier parameter:

import org.checkerframework.checker.tainting.qual.Tainted;
import org.checkerframework.framework.qual.HasQualifierParameter;
import org.checkerframework.checker.tainting.qual.Untainted;

class MyBuffer extends Buffer {

  public void method1(@Tainted MyBuffer b1, @Untainted MyBuffer b2) {
    b1 = b2;  // error
  }

  public void method2(@Tainted Buffer b1, @Untainted Buffer b2) {
    b1 = b2;  // error
  }
}

@HasQualifierParameter(Tainted.class)
public class Buffer {}