ConstraintSolver::coerceToRValue() missed a bunch of cases where we
should be dealing with lvalues, e.g., tuples, "try" expressions, and
so on. Extend TypeChecker::coerceToRValue() to deal with the
expression type side-tables and ConstraintSolver::coerceToRValue() to
it.
Fixes rdar://problem/32700180, a crash-on-valid.
