test: add integration test for side effects (#29329)

This new tests keeps track of the known side effects for Angular ES modules.

PR Close #29329

integration/side-effects/snapshots/forms/esm2015.js

@@ -0,0 +1,7 @@
+import "@angular/core";
+
+import "@angular/platform-browser";
+
+import "rxjs";
+
+import "rxjs/operators";