components: Change component loading to be asynchronous

Some components use build time optional dependencies such as
GNOME Bluetooth, so we need to import the components
conditionally.

Also rename to get rid of __init__.js file

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1499>

js/ui/components.js

@@ -0,0 +1,62 @@
+/* exported ComponentManager */
+const Main = imports.ui.main;
+
+var ComponentManager = class {
+    constructor() {
+        this._allComponents = {};
+        this._enabledComponents = [];
+
+        Main.sessionMode.connect('updated', () => {
+            this._sessionModeUpdated().catch(logError);
+        });
+
+        this._sessionModeUpdated().catch(logError);
+    }
+
+    async _sessionModeUpdated() {
+        let newEnabledComponents = Main.sessionMode.components;
+
+        await Promise.allSettled([...newEnabledComponents
+            .filter(name => !this._enabledComponents.includes(name))
+            .map(name => this._enableComponent(name))]);
+
+        this._enabledComponents
+            .filter(name => !newEnabledComponents.includes(name))
+            .forEach(name => this._disableComponent(name));
+
+        this._enabledComponents = newEnabledComponents;
+    }
+
+    async _importComponent(name) {
+        // TODO: Import as module
+        let module = await imports.ui.components[name];
+        return module.Component;
+    }
+
+    async _ensureComponent(name) {
+        let component = this._allComponents[name];
+        if (component)
+            return component;
+
+        if (Main.sessionMode.isLocked)
+            return null;
+
+        let constructor = await this._importComponent(name);
+        component = new constructor();
+        this._allComponents[name] = component;
+        return component;
+    }
+
+    async _enableComponent(name) {
+        let component = await this._ensureComponent(name);
+        if (component)
+            component.enable();
+    }
+
+    _disableComponent(name) {
+        let component = this._allComponents[name];
+        if (component == null)
+            return;
+        component.disable();
+    }
+};