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

tests/compiler/dart2js/cps_ir/input/argument_refinement_num_15.dart

Index: tests/compiler/dart2js/cps_ir/input/argument_refinement_num_15.dart
diff --git a/tests/compiler/dart2js/cps_ir/input/argument_refinement_num_15.dart b/tests/compiler/dart2js/cps_ir/input/argument_refinement_num_15.dart
new file mode 100644
index 0000000000000000000000000000000000000000..227e62e2d7e727a6ba27c621050ddba6fea2d77d
--- /dev/null
+++ b/tests/compiler/dart2js/cps_ir/input/argument_refinement_num_15.dart
@@ -0,0 +1,12 @@
+main() {
+  var x = int.parse('1233');
+  var y = int.parse('1234');
+  var z = int.parse('1236');
+  print(x is num);
+  print(y is num);
+  print(z is num);
+  print(x.clamp(y, z));
+  print(x is num);
+  print(y is num); // will be compiled to `true` if we know the type of `y`.
+  print(z is num);
+}