Delay constraint generation for capture list until body of
the associated closure is resolved. This means that we can
unify capture checking with that of regular pattern bindings
for multi-statement closures.
Implicit casts are allowed to provide cast type directly without
a type repr, adjust solution application logic to handle this just
like constraint generator does. Also fix a couple of places where
declaration context from constraint system was used instead
of one associated with the expression rewriter.
Implicit casts are allowed to be constructed with a type, instead
of a type repr. Constraint generation should honor that, and fallback
to using cast type when repr is was not given.
