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

tests/compiler/dart2js/cps_ir/input/supercall_2.dart

+// 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;
+}