Fix desugaring of classes with context bounds
Fix desugaring of classes with context bounds

Context bounds did not make it before into secondary
constructors. Now the evidence parameters generated
by context bounds get copied into secondary constructors.

Without this fix, scala.collection.immutable.PagedSeq fails
to compile in new classtag scheme.

som-snytt/dotty,sjrd/dotty,dotty-staging/dotty,som-snytt/dotty,som-snytt/dotty,dotty-staging/dotty,sjrd/dotty,dotty-staging/dotty,som-snytt/dotty,lampepfl/dotty,lampepfl/dotty,dotty-staging/dotty,sjrd/dotty,lampepfl/dotty,lampepfl/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,som-snytt/dotty,dotty-staging/dotty