Constraint generation uses a special pattern while generating
constraints for assignments to make sure that the source type
is convertible to r-value type of the destination.
`BindingSet::favoredOverDisjunction` needs to recognize this
pattern, where disjunction type variable is bound early, and
avoid prioritizing closure if it's connected to the "fixed type"
of the disjunction or risk losing annotations associated with
the member such as `@Sendable` or a global actor.
Resolves: rdar://131524246
