[kernel] Support for top-level generic functions.

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

 library;
 import self as self;
 import "dart:core" as core;
 
 class C extends core::Object {
   field dynamic f = MakeClosure<() → dynamic>(self::closure#C#f#function, null);
   default constructor •() → void
     : super core::Object::•()
     ;
   get g() → dynamic {
@@ skipping 32 matching lines @@
   method d(dynamic x, {dynamic y = 2}) → dynamic {
     return x.+(y);
   }
 }
 class E<T extends core::Object> extends core::Object {
   field dynamic f = MakeClosure<() → dynamic>(self::closure#E#f#function, null);
   default constructor •() → void
     : super core::Object::•()
     ;
   get g() → dynamic {
-    return MakeClosure<<T extends core::Object>(T) → dynamic, self::E::T>(self::closure#E#g#function, null);
+    return MakeClosure<<T extends core::Object>(T) → dynamic, self::E::T>(self::closure#E#g#function, MakeVector(1));
   }
   method a() → dynamic {
     return "a";
   }
   method b(self::E::T x) → dynamic {
     return x;
   }
   method c(self::E::T x, [self::E::T y = 2]) → dynamic {
     return x.+(y);
   }
@@ skipping 42 matching lines @@
 }
 static method closure#D#f#function(Vector #contextParameter) → dynamic {
   return "f";
 }
 static method closure#E#g#function<T extends core::Object>(Vector #contextParameter, self::closure#E#g#function::T x) → dynamic {
   return "g(${x})";
 }
 static method closure#E#f#function(Vector #contextParameter) → dynamic {
   return "f";
 }