Explicitly convert raw data to strings

As strings are guaranteed to use UTF-8 in the GNOME platform, generic
file APIs like g_file_load_contents() return raw data instead. Since
gjs' recent update to mozjs60, this data is now returns as Uint8Array
which cannot simply be treated as string - its toString() method boils
down to arr.join(',') - so use gjs' new ByteArray module to explicitly
convert the data.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/179

js/misc/extensionUtils.js

@@ -112,6 +112,8 @@ function createExtensionObject(uuid, dir, type) {
     let metadataContents, success, tag;
     try {
         [success, metadataContents, tag] = metadataFile.load_contents(null);
+        if (metadataContents instanceof Uint8Array)
+            metadataContents = imports.byteArray.toString(metadataContents);
     } catch (e) {
         throw new Error('Failed to load metadata.json: ' + e);
     }