Add session managment to masquerade module to allow testing switching between multiple users at the same time.

Hello. We have always used this module and think it is one of the most essential modules to have in Drupal. But once I started testing on a Drupal website that contains multiple roles who interact with each other, I started to wish for the ability to switch between sessions very fast, for example, I can select 3 users, hit masquerade, go to user 1, do a couple of things, then, there will maybe be a small floating button at the corner, I can click it, and switch to the other users very fast (I can, for example, switch to user 2), and if I wanted, I can return to the original user (usually the root), and do a couple of things, without losing the other session, I can still click the small button and just switch and comeback to user 1, and just redo the testing.

I think this feature requires some rewriting on the module, so I guess we need some opinions on this. Thank you.