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

tests/compiler/dart2js/cps_ir/input/argument_refinement_28.dart

+import 'dart:math';
+main() {
+  var x = int.parse('3');
+  var y = int.parse('1234');
+  var z = int.parse('1236');
+  var w = int.parse('2');
+  print(x is num);
+  print(sin(x));
+  print(x is num);
+
+  print(y is num);
+  print(log(y));
+  print(y is num);
+
+  print(z is num);
+  print(w is num);
+  print(pow(z, w));
+  print(z is num);
+  print(w is num);
+}