By direclty using the underlying GSetting, whether or not an extension
appears as enabled or disabled currently depends only on whether it is
included in the 'enabled-extensions' list or not.
However this doesn't necessarily reflect the real extension state, as an
extension may be in error state, or enabled via the session mode.
Switch to the extensions D-Bus API to ensure that the list of extensions
and each extension's state correctly reflects the state in gnome-shell.