[TG-21232] Add @InTestsUseFactory annotation

[pcrane]

Adds a new annotation to point Diffblue Cover to factories that could be used when writing tests for a given method.

For example:

public class ThingFactory {
  public static Thing factory(){
    return new Thing();
  }
}

public class Foo {
  @InTestsUseFactory(className="ThingFactory", methodName="factory")
  public void doThing(Thing t){
    // ...
  }
}

[roxspring]

Other annotations are named in the plural so this stands out. We should consider switching to plural naming.