View focused activity.

def view_focused_activity(self) -> str:
        '''View focused activity.'''
        output, _ = self._execute(
            '-s', self.device_sn, 'shell', 'dumpsys', 'activity', 'activities')
        return re.findall(r'mFocusedActivity: .+(com[a-zA-Z0-9\.]+/.[a-zA-Z0-9\.]+)', output)[0]