Adopt EventEmitter class instead of injecting Signal methods

Introduce a new class, EventEmitter, which implements signal
handling for pure JavaScript classes. EventEmitter still
utilizes GJS' addSignalMethods internally.

EventEmitter allows static typechecking to understand the
structure of event-emitting JS classes and makes creating
child classes simpler.

The name 'EventEmitter' mirrors a common name for this pattern
in Node and in JS libraries.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2043>

js/gdm/batch.js

@@ -43,12 +43,15 @@
  * are not used elsewhere. These APIs may ultimately get dropped entirely and
  * replaced by something else.
  */
+/* exported ConcurrentBatch, ConsecutiveBatch */
 
 const { GObject } = imports.gi;
-const Signals = imports.signals;
+const Signals = imports.misc.signals;
 
-var Task = class {
+var Task = class extends Signals.EventEmitter {
     constructor(scope, handler) {
+        super();
+
         if (scope)
             this.scope = scope;
         else
@@ -64,7 +67,6 @@ var Task = class {
         return null;
     }
 };
-Signals.addSignalMethods(Task.prototype);
 
 var Hold = class extends Task {
     constructor() {
@@ -101,7 +103,6 @@ var Hold = class extends Task {
         return this._acquisitions > 0;
     }
 };
-Signals.addSignalMethods(Hold.prototype);
 
 var Batch = class extends Task {
     constructor(scope, tasks) {
@@ -171,7 +172,6 @@ var Batch = class extends Task {
         this.tasks = this.tasks.splice(0, this._currentTaskIndex + 1);
     }
 };
-Signals.addSignalMethods(Batch.prototype);
 
 var ConcurrentBatch = class extends Batch {
     process() {
@@ -186,7 +186,6 @@ var ConcurrentBatch = class extends Batch {
         this.nextTask();
     }
 };
-Signals.addSignalMethods(ConcurrentBatch.prototype);
 
 var ConsecutiveBatch = class extends Batch {
     process() {
@@ -205,4 +204,3 @@ var ConsecutiveBatch = class extends Batch {
         }
     }
 };
-Signals.addSignalMethods(ConsecutiveBatch.prototype);

js/gdm/credentialManager.js

@@ -1,8 +1,12 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported CredentialManager */
 
-var CredentialManager = class CredentialManager {
+const Signals = imports.misc.signals;
+
+var CredentialManager = class CredentialManager extends Signals.EventEmitter {
     constructor(service) {
+        super();
+
         this._token = null;
         this._service = service;
         this._authenticatedSignalId = null;

js/gdm/oVirt.js

@@ -2,7 +2,6 @@
 /* exported getOVirtCredentialsManager */
 
 const Gio = imports.gi.Gio;
-const Signals = imports.signals;
 const Credential = imports.gdm.credentialManager;
 
 var SERVICE_NAME = 'gdm-ovirtcred';
@@ -43,7 +42,6 @@ var OVirtCredentialsManager = class OVirtCredentialsManager extends Credential.C
             });
     }
 };
-Signals.addSignalMethods(OVirtCredentialsManager.prototype);
 
 function getOVirtCredentialsManager() {
     if (!_oVirtCredentialsManager)

js/gdm/realmd.js

@@ -1,7 +1,8 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+/* exported Manager */
 
 const Gio = imports.gi.Gio;
-const Signals = imports.signals;
+const Signals = imports.misc.signals;
 
 const { loadInterfaceXML } = imports.misc.fileUtils;
 
@@ -14,8 +15,10 @@ const Service = Gio.DBusProxy.makeProxyWrapper(ServiceIface);
 const RealmIface = loadInterfaceXML("org.freedesktop.realmd.Realm");
 const Realm = Gio.DBusProxy.makeProxyWrapper(RealmIface);
 
-var Manager = class {
+var Manager = class extends Signals.EventEmitter {
     constructor() {
+        super();
+
         this._aggregateProvider = Provider(Gio.DBus.system,
                                            'org.freedesktop.realmd',
                                            '/org/freedesktop/realmd',
@@ -105,4 +108,3 @@ var Manager = class {
         this._updateLoginFormat();
     }
 };
-Signals.addSignalMethods(Manager.prototype);

js/gdm/util.js

@@ -1,9 +1,10 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported BANNER_MESSAGE_KEY, BANNER_MESSAGE_TEXT_KEY, LOGO_KEY,
-            DISABLE_USER_LIST_KEY, fadeInActor, fadeOutActor, cloneAndFadeOutActor */
+            DISABLE_USER_LIST_KEY, fadeInActor, fadeOutActor, cloneAndFadeOutActor,
+            ShellUserVerifier */
 
 const { Clutter, Gdm, Gio, GLib } = imports.gi;
-const Signals = imports.signals;
+const Signals = imports.misc.signals;
 
 const Batch = imports.gdm.batch;
 const OVirt = imports.gdm.oVirt;
@@ -135,8 +136,9 @@ function cloneAndFadeOutActor(actor) {
     return hold;
 }
 
-var ShellUserVerifier = class {
+var ShellUserVerifier = class extends Signals.EventEmitter {
     constructor(client, params) {
+        super();
         params = Params.parse(params, { reauthenticationOnly: false });
         this._reauthOnly = params.reauthenticationOnly;
 
@@ -783,4 +785,3 @@ var ShellUserVerifier = class {
         this._verificationFailed(serviceName, true);
     }
 };
-Signals.addSignalMethods(ShellUserVerifier.prototype);

js/gdm/vmware.js

@@ -2,7 +2,6 @@
 /* exported getVmwareCredentialsManager */
 
 const Gio = imports.gi.Gio;
-const Signals = imports.signals;
 const Credential = imports.gdm.credentialManager;
 
 const dbusPath = '/org/vmware/viewagent/Credentials';
@@ -46,7 +45,6 @@ var VmwareCredentialsManager = class VmwareCredentialsManager extends Credential
             });
     }
 };
-Signals.addSignalMethods(VmwareCredentialsManager.prototype);
 
 function getVmwareCredentialsManager() {
     if (!_vmwareCredentialsManager)