extensionSystem: Include dir and path in data passed to extension

Extensions often need to set up additional resources from their
directory, like settings, translations or image assets.

So far extensions have used getCurrentExtension() to access the
shell's internal extension object which contains path and dir
properties. That's far from ideal, first because it requires
generating a stack to figure out the current extension, and
second because the internal object also contains state that
extensions shouldn't meddle with.

Just include those properties in the metadata we pass to the
extension constructor.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2838>

js/ui/extensionSystem.js

@@ -536,7 +536,9 @@ var ExtensionManager = class extends Signals.EventEmitter {
         }
 
         try {
-            extensionState = new extensionModule.default(extension.metadata);
+            const {metadata, path} = extension;
+            extensionState =
+                new extensionModule.default({...metadata, dir, path});
         } catch (e) {
             this.logExtensionError(uuid, e);
             return false;