Nullness markers to enable flattening

[Dan Smith]

> On Mar 2, 2023, at 6:21 AM, Gernot Neppert <mcnepp02 at googlemail.com> wrote:
> 
> The following two lines are quotes from Dan's list of "key ideas": - Nullness is an *optional* property of variables/expressions/etc., distinct from types.
> - Type variable types have nullness, too.
> 
> 
> To me, this looks a little contradictory. If we agree on the first statement (and I do agree with it),
> 
> then Type-variables should not have an attached nullness-marker.
> 
> Rather, each _use_ of a Type-variable in a generic class would have the attached nullness.

That's the intent. By "type variable types", I mean type variable uses.