Linker should warn about usage of MakeGenericType/MakeGenericMethod

When using MakeGenericType and MakeGenericMethod trimmer should warn if the callable method is known and is annotated with RequiresUnreferencedCode. For example:
```C#
class GenericWithConstraint where T : new() {
public static void Generic (T toDisplay) { }
}

class ClassWithRequiresUnreferencedCodeOnConstructor {
[RequiresUnreferencedCode ("Message for --ClassWithRequiresUnreferencedCodeOnCostructor--")]
void ClassWithRequiresUnreferencedCodeOnCostructor () { }
}
static void Main () {
Type generic = typeof (GenericWithConstraint<>);
Type constructed = generic.MakeGenericType (typeof (ClassWithRequiresUnreferencedCodeOnConstructor));
}
```
In this case the generic class has the new constraint and the type ClassWithRequiresUnreferencedCodeOnConstructor is recognized inside the ReflectionMethodBodyScanner. Trimmer should be able to understand that the constructor will be called and since is annotated produce a warning.