Add support for converted closures with explicit contexts to VM

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

 library;
 import self as self;
 import "dart:core" as core;
 
 class C<T extends core::Object, S extends core::Object> extends core::Object {
   constructor internal() → void
     : super core::Object::•()
     ;
   method foo(self::C::S s) → dynamic {
     final Vector #context = MakeVector(2);
     #context[1] = this;
     return MakeClosure<(dynamic) → dynamic>(self::closure#C#foo#function, #context);
   }
   method bar() → dynamic {
     self::C<self::C::T, self::C::S> self = this;
   }
   method baz() → dynamic {
-    return MakeClosure<() → () → self::C<dynamic, dynamic>>(self::closure#C#baz#function, null);
+    return MakeClosure<() → dynamic>(self::closure#C#baz#function, null);
   }
   static factory •<T extends core::Object, S extends core::Object>() → self::C<self::C::•::T, self::C::•::S> {
     final () → dynamic local = MakeClosure<() → dynamic>(self::closure#C#function#local, null);
     return local.call();
   }
 }
 static method main(dynamic arguments) → dynamic {
   core::print(self::C::•<core::String, core::String>().foo(null).call(arguments.first));
   dynamic c = self::C::•<core::int, core::int>().baz().call().call();
   if(!(c is self::C<core::int, core::int>))
     throw "${c} fails type test 'is C<int, int>'";
   if(c is self::C<core::String, core::String>) {
     throw "${c{self::C<core::String, core::String>}} passes type test 'is C<String, String>'";
   }
   core::print(c);
 }
 static method closure#C#foo#function(Vector #contextParameter, dynamic x) → dynamic {
   dynamic y = x;
   core::Object z = y;
   self::C<dynamic, dynamic> self = #contextParameter[1];
   return z as dynamic;
 }
-static method closure#C#baz#function#function(Vector #contextParameter) → self::C<dynamic, dynamic> {
+static method closure#C#baz#function#function(Vector #contextParameter) → dynamic {
   return self::C::•<dynamic, dynamic>();
 }
-static method closure#C#baz#function(Vector #contextParameter) → () → self::C<dynamic, dynamic> {
-  return MakeClosure<() → self::C<dynamic, dynamic>>(self::closure#C#baz#function#function, #contextParameter);
+static method closure#C#baz#function(Vector #contextParameter) → dynamic {
+  return MakeClosure<() → dynamic>(self::closure#C#baz#function#function, #contextParameter);
 }
 static method closure#C#function#local(Vector #contextParameter) → dynamic {
   self::C<dynamic, dynamic> self = new self::C::internal<dynamic, dynamic>();
   return self;
 }