Fix many bugs with closure conversion in checked mode.

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

 library;
 import self as self;
 
 static field dynamic v;
 static method main(dynamic arguments) → dynamic {
-  final Vector #context = MakeVector(3);
+  final dynamic #context = MakeVector(3);
   #context[2] = null;
   (MakeClosure<(dynamic) → dynamic>(self::closure#main#function, #context)).call(87);
   if(!self::v.==(87)) {
     throw "Unexpected value in v: ${self::v}";
   }
   if(!(#context[2]).==(87)) {
     throw "Unexpected value in w: ${#context[2]}";
   }
   self::v = true;
   (MakeClosure<() → dynamic>(self::closure#main#function#1, #context)).call();
   if(!self::v.==(false)) {
     throw "Unexpected value in v: ${self::v}";
   }
   if(!(#context[2]).==(false)) {
     throw "Unexpected value in w: ${#context[2]}";
   }
 }
-static method closure#main#function(Vector #contextParameter, dynamic x) → dynamic {
+static method closure#main#function(dynamic #contextParameter, dynamic x) → dynamic {
   return self::v = #contextParameter[2] = x;
 }
-static method closure#main#function#1(Vector #contextParameter) → dynamic {
+static method closure#main#function#1(dynamic #contextParameter) → dynamic {
   for (; #contextParameter[2] = self::v; ) {
     self::v = false;
   }
 }