environment: Port environment.js to be an ES module

Removes the init() function in favor of executing all environment
changes when the file is imported.

Additionally ports all unit tests using imports.gi.environment.init() to
use the updated module.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2822>

js/ui/init.js

@@ -1,10 +1,7 @@
-import {setConsoleLogDomain} from 'console';
 import GLib from 'gi://GLib';
 import Gio from 'gi://Gio';
 
-setConsoleLogDomain('GNOME Shell');
-
-imports.ui.environment.init();
+import './environment.js';
 
 // Run the Mutter main loop after
 // GJS finishes resolving this module.