cpsir unittests: move all unittests into individual files and test runners.

tests/compiler/dart2js/cps_ir/expected/supercall_2.js

+// Expectation for test: 
+// // TODO(sigmund): change this to check method "function(Sub#+)" once we provide
+// // a way to disable inlining of Sub#+, which is compiled to something like:
+// // function(x) {
+// //   var v0, v1, v2;
+// //   v0 = 1;
+// //   v1 = J.getInterceptor$ns(x).$add(x, v0);
+// //   v2 = this;
+// //   return V.Base.prototype.$add.call(null, v2, v1);
+// // }
+// 
+// class Base {
+//   m(x) {
+//     print(x+1000);
+//   }
+//   operator+(x) => m(x+10);
+// }
+// class Sub extends Base {
+//   m(x) => super.m(x+100);
+//   operator+(x) => super + (x+1);
+// }
+// main() {
+//   new Sub() + 10000;
+// }
+
+function() {
+  var v0 = V.Sub$();
+  V.Base.prototype.$add.call(v0, v0, 10000 + 1);
+}