Compatability with Admin themes such as Gin

Looking over https://www.drupal.org/project/userswitch/issues/3087885 ✨ Add an entity operation instead of a user list Needs review , I am seeing a number of comments about not seeing the 'Back to account' link in the menu that should allow an admin to be able to switch back to their main account.

I'm not sure what other Admin themes people are using, but we are using Gin and currently encountering this issue.

I believe this is because of the use of the `toolbar-icon-escape-admin` class on the inserted menu item. That class is also used for the 'Back to site' link that goes back to the last non-admin page visited. I'm assuming this was chosen so that the link would inherit the same icon.

However, in the Gin theme, they hide the main 'Back to site' link and replicate it elsewhere in the theme. This activity is also inadvertently hiding the UserSwitch link. Using a custom class for the link would fix the hiding issue, but would then probably need to supply a dedicated icon as well.