Fixes to subtyping tests for constrained parameters.
Fixes to subtyping tests for constrained parameters.

1. When testing A <:< B where A and B are both in the current constraint set, we used to do a A <:< L first, where L is the lower bound of B. But that gives the wrong upper bound to A, it should be B instead of L!. This comment corrects that.

2. Again when testing A <:< B we need to record B as an upper bound of A, but also record A as a lower bound of B. That way, either instantiation of A and B will propagate correctly. If we dod not do that and just recorded B as upper bound of A, we could then minimize B to Nothing, so A would be forced to Nothing as well. This is clearly wrong. We should have minimized B to A instead.

vsalvis/dotty,AlexSikia/dotty,spetz911/dotty,dotty-staging/dotty,som-snytt/dotty,svalaskevicius/dotty,yusuke2255/dotty,angi2/dotty,som-snytt/dotty,auvik/dotty,som-snytt/dotty,DarkDimius/dotty,lampepfl/dotty,yusuke2255/dotty,svalaskevicius/dotty,sjrd/dotty,som-snytt/dotty,AlexSikia/dotty,folone/dotty,lampepfl/dotty,densh/dotty,densh/dotty,lampepfl/dotty,dotty-staging/dotty,vsalvis/dotty,reactormonk/dotty,reactormonk/dotty,VladimirNik/dotty,sjrd/dotty,angi2/dotty,sjrd/dotty,auvik/dotty,folone/dotty,sjrd/dotty,VladimirNik/dotty,dotty-staging/dotty,spetz911/dotty,som-snytt/dotty,lampepfl/dotty,dotty-staging/dotty,dotty-staging/dotty,sjrd/dotty,lampepfl/dotty