extensions: Provide separate implementations

For the time being this mostly means re-exporting functions
from the shared module. However openPrefs() is now only
available to extensions, and we stop exporting both
getCurrentExtension() and setExtensionManager() to either
extensions or prefs.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2837>

js/extensions/extension.js

@@ -0,0 +1,28 @@
+import {getCurrentExtension} from './sharedInternals.js';
+
+export {
+    getSettings,
+    initTranslations,
+    gettext,
+    ngettext,
+    pgettext
+} from './sharedInternals.js';
+
+/**
+ * Open the preference dialog of the current extension
+ */
+export function openPrefs() {
+    const extension = getCurrentExtension();
+
+    if (!extension)
+        throw new Error('openPrefs() can only be called from extensions');
+
+    try {
+        const extensionManager = imports.ui.main.extensionManager;
+        extensionManager.openExtensionPrefs(extension.uuid, '', {});
+    } catch (e) {
+        if (e.name === 'ImportError')
+            throw new Error('openPrefs() cannot be called from preferences');
+        logError(e, 'Failed to open extension preferences');
+    }
+}