Address gjs libraries deprecation warnings

[alessandrodolci]

Last versions of Gnome Shell came with some changes to gjs libraries, which currently cause some warning messages to be thrown regarding some of the extension components.
Here is a brief description of the issues:

• The output of some GObject functions has been changed from the custom ByteArray type to JS Uint8Array built-in type, as reported here: https://gitlab.gnome.org/GNOME/gjs/-/tags/1.53.90.

  • Obtaining a string representation of such types objects should now be done by explicitly calling the ByteArray toString method.

• Access and usage of the actor property on UI GObject instances has been deprecated

  • We do so inside the DockerMenu and DockerSubMenuMenuItem classes, this should be addressed calling methods directly on the instance, instead of obtaining the actor property reference first.

Both of the issues have a warning status, not causing any break for the time being, but support of the old behaviors is not guaranteed by the libraries, so fixes should be applied to avoid further issues.