theme: Remove icon resources from theme

- move all icons to the icons directory
- rename some icons to be more meaningful
- put all icons on a resource sheet
- update references to icon name changes
- deprecate icons for those in standard set

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2141>

js/ui/main.js

@@ -98,6 +98,7 @@ let _defaultCssStylesheet = null;
 let _cssStylesheet = null;
 let _themeResource = null;
 let _oskResource = null;
+let _iconResource = null;
 
 Gio._promisify(Gio._LocalFilePrototype, 'delete_async', 'delete_finish');
 Gio._promisify(Gio._LocalFilePrototype, 'touch_async', 'touch_finish');
@@ -189,6 +190,7 @@ function _initializeUI() {
     Shell.AppUsage.get_default();
 
     reloadThemeResource();
+    _loadIcons();
     _loadOskLayouts();
     _loadDefaultStylesheet();
 
@@ -440,6 +442,12 @@ function reloadThemeResource() {
     _themeResource._register();
 }
 
+/** @private */
+function _loadIcons() {
+    _iconResource = Gio.Resource.load('%s/gnome-shell-icons.gresource'.format(global.datadir));
+    _iconResource._register();
+}
+
 function _loadOskLayouts() {
     _oskResource = Gio.Resource.load('%s/gnome-shell-osk-layouts.gresource'.format(global.datadir));
     _oskResource._register();