Add primitive to create closures and use it for closure conversion

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 new self::Closure#C1##function::•(#context), super core::Object::•()
+    : self::C1::x = let final Vector #context = MakeVector(2) in let dynamic #t1 = #context[1] = y in MakeClosure<() → dynamic>(self::closure#C1##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);
     #context[1] = y;
-    this.x = new self::Closure#C2#function#function::•(#context);
-  }
-}
-class Closure#C1##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#C1##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#C1##function::context};
-    return core::print("Hello ${#contextParameter[1]}");
-  }
-}
-class Closure#C2#function#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#C2#function#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#C2#function#function::context};
-    return core::print("Hello ${#contextParameter[1]}");
+    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(Vector #contextParameter) → dynamic {
+  return core::print("Hello ${#contextParameter[1]}");
+}
+static method closure#C2#function#function(Vector #contextParameter) → dynamic {
+  return core::print("Hello ${#contextParameter[1]}");
+}