build: fix unit test local target being killed by ibazel watcher

Currently when trying to debug a unit test locally using
the Bazel `_local` target for web tests, the Karma instance
is getting killed (if the test runs without ibazel) due to
the Karma iBazel watcher being registered accidentally.

We fixed this in the past by disabling the watcher, but
the Karma NodeJS rules have changed and we need to adjust
our monkey-patch so that the watcher is not registered.

(cherry picked from commit 384ce51)

Author: devversion

test/bazel-karma-local-config.js

@@ -3,8 +3,6 @@
  * want to launch any browser and just enable manual browser debugging.
  */
 
-const bazelKarma = require('@bazel/concatjs');
-
 module.exports = config => {
   const overwrites = {};
 
@@ -30,8 +28,21 @@ module.exports = config => {
   // relies on ibazel to write to the `stdin` interface. When running without ibazel, the
   // watcher will kill concatjs since there is no data written to the `stdin` interface.
   if (process.env['IBAZEL_NOTIFY_CHANGES'] !== 'y') {
-    delete bazelKarma['watcher'];
+    // We pre-define a plugins array that captures registration of Karma plugins
+    // and unsets the watcher definitions so that no watcher can be configured.
+    overwrites.plugins = new KarmaPluginArrayWithoutWatchers();
   }
 
   config.set(overwrites);
 };
+
+class KarmaPluginArrayWithoutWatchers extends Array {
+  // The Bazel Karma rules only register new plugins using `.push`.
+  push(...plugins) {
+    plugins
+      .filter(p => typeof p === 'object')
+      .forEach(p => delete p.watcher);
+
+    super.push(...plugins);
+  }
+}