Add support for converted closures with explicit contexts to VM

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

 library;
 import self as self;
 import "dart:core" as core;
 
 class C1 extends core::Object {
   field dynamic x;
   constructor •(dynamic y) → void
-    : self::C1::x = let final Vector #context = MakeVector(2) in let dynamic #t1 = #context[1] = y in MakeClosure<() → dynamic>(self::closure#C1#function#function, #context), super core::Object::•()
+    : final Vector #context = MakeVector(2), dynamic #t1 = #context[1] = y, self::C1::x = MakeClosure<() → dynamic>(self::closure#C1#function#function, #context), super core::Object::•()
     ;
 }
 class C2 extends core::Object {
   field dynamic x = null;
   constructor •(dynamic y) → void
-    : super core::Object::•() {
+    : final Vector #context = MakeVector(2), dynamic #t2 = #context[1] = y, super core::Object::•() {
     final Vector #context = MakeVector(2);
     #context[1] = y;
-    this.x = MakeClosure<() → void>(self::closure#C2#function#function, #context);
+    this.x = MakeClosure<() → dynamic>(self::closure#C2#function#function, #context);
   }
 }
 static method main() → dynamic {
   new self::C1::•("hest").x();
   new self::C2::•("naebdyr").x();
 }
 static method closure#C1#function#function(Vector #contextParameter) → dynamic {
   return core::print("Hello ${#contextParameter[1]}");
 }
-static method closure#C2#function#function(Vector #contextParameter) → void {
+static method closure#C2#function#function(Vector #contextParameter) → dynamic {
   return core::print("Hello ${#contextParameter[1]}");
 }