Add primitive to create closures and use it for closure conversion

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

 library;
 import self as self;
 import "dart:core" as core;
 
 class C extends core::Object {
   field dynamic t;
   constructor foo(dynamic f) → void
-    : self::C::t = let final Vector #context = MakeVector(2) in let dynamic #t1 = #context[1] = f in new self::Closure#C#foo#function::•(#context), super core::Object::•() {
+    : self::C::t = let final Vector #context = MakeVector(2) in let dynamic #t1 = #context[1] = f in MakeClosure<() → dynamic>(self::closure#C#foo#function, #context), super core::Object::•() {
     final Vector #context = MakeVector(2);
     #context[1] = f;
     core::print(1);
   }
 }
-class Closure#C#foo#function extends core::Object implements core::Function {
-  field core::String note = "This is temporary. The VM doesn't need closure classes.";
-  field Vector context;
-  constructor •(final Vector context) → dynamic
-    : self::Closure#C#foo#function::context = context
-    ;
-  method call() → dynamic {
-    "This is a temporary solution. In the VM, this will become an additional parameter.";
-    final Vector #contextParameter = this.{self::Closure#C#foo#function::context};
-    return (#contextParameter[1]).call();
-  }
-}
-class Closure#main#function extends core::Object implements core::Function {
-  field core::String note = "This is temporary. The VM doesn't need closure classes.";
-  field Vector context;
-  constructor •(final Vector context) → dynamic
-    : self::Closure#main#function::context = context
-    ;
-  method call() → dynamic {
-    "This is a temporary solution. In the VM, this will become an additional parameter.";
-    final Vector #contextParameter = this.{self::Closure#main#function::context};
-    return core::print("hest");
-  }
-}
 static method main() → dynamic {
   core::print(0);
-  dynamic c = new self::C::foo(new self::Closure#main#function::•(null));
+  dynamic c = new self::C::foo(MakeClosure<() → dynamic>(self::closure#main#function, null));
   core::print(2);
   c.t();
   core::print(3);
 }
+static method closure#C#foo#function(Vector #contextParameter) → dynamic {
+  return (#contextParameter[1]).call();
+}
+static method closure#main#function(Vector #contextParameter) → dynamic {
+  return core::print("hest");
+}