Panel cleanup 2 (#13613)

* panel.js: Remove the TextShadower object

This isn't used anywhere in Cinnamon or any Xlets.

* panel.js: Port the PanelManager to GObject

Clean up uses of Lang.bind() and clean up a few variable names and some code
styling

* panel.js: Port the PanelDummy to GObject

This removes a use of CinnamonGenericContainer

* panel.js: Remove the AnimatedIcon object

We only have one unmaintained applet using this currently. For the use case
of a spinner, we can add a dedicated object for that purpose. We have other
uses for that.

* panel.js: Port the SettingsLauncher object to a class

Remove usage of Lang.bind() as well

* panel.js: Port the PanelContextMenu to class

Remove old commented out options. These have been disabled for a long time.
They can be re-added if we want to bring them back.

* panel.js: Port the PanelZoneDNDHandler to class

* panel.js: Port the Panel object to class

* Rebase on git master

* panel.js: Port the panel to St.Widget

This removes another major use of CinnamonGenericContainer. This could be
taken even further, but trying to break as little as possible with this
change.

* panel.js: Clean up a bit of code styling

This is only a partial cleanup. This file is a mess of different styles
but hopefully it's at least a bit better.

* panel.js: Remove unneeded uses of this.actor

* appletManager.js: Fixed a typo in variable name

Missed this when converting the panel to an St.Widget

Author: JosephMcc

js/ui/applet.js

@@ -656,7 +656,7 @@ var Applet = class Applet {
     }
 
     get _panelHeight() {
-        return this.panel.height;
+        return this.panel.heightForZones;
     }
 
     get _scaleMode() {

js/ui/appletManager.js

@@ -597,7 +597,7 @@ function createApplet(extension, appletDefinition, panel = null) {
         // FIXME: Panel height is now available before an applet is initialized,
         // so we don't need to pass it to the constructor anymore, but would
         // require a compatibility clean-up effort.
-        applet = extension.module.main(extension.meta, orientation, panel.height, applet_id);
+        applet = extension.module.main(extension.meta, orientation, panel.heightForZones, applet_id);
     } catch (e) {
         Extension.logError(`Failed to evaluate 'main' function on applet: ${uuid}/${applet_id}`, uuid, e);
         return null;