Add support for converted closures with explicit contexts to VM

pkg/kernel/testcases/closures/contexts_in_super_initializers.dart.expect

 library;
 import self as self;
 import "dart:core" as core;
 
 class X extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     : super core::Object::•()
     ;
 }
 class Y extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     : super core::Object::•()
     ;
 }
 class A extends core::Object {
   field self::X x;
   field self::Y y;
   constructor •(self::X x, self::Y y) → void
     : self::A::x = x, self::A::y = y, super core::Object::•()
     ;
 }
 class B extends self::A {
   constructor •(self::X x, self::Y y) → void
     : super self::A::•(x, y) {}
 }
 static method main() → dynamic {
   self::B b = new self::B::•(new self::X::•(), new self::Y::•());
 }