Add "indeterminate" state to Switch component

[is-jonreeves]

Feature request

Overview

Checkboxes allow for an indeterminate state, and Radix Switches appear to use checkboxes under-the-hood. It would be good to expose this option and provide a visual change to represent it.

It would be useful in "batch edit" scenarios where you are controlling the value for multiple subjects at once. For example, selecting Multiple Users and then toggling an option for all of them.

Examples in other libraries

A Google Images search surfaces a bunch of examples of indeterminate Switches/Toggles, but honestly I didn't find many UI libraries in the React space that cater for it.

Additional context

It doesn't seem too common, so I'm doubtful its a wise UX pattern to encourage (I suspect a real checkbox is more appropriate in the scenario I laid out above). BUT... if your UI is already designed and implemented around Switches, having this feature as an option would be useful, otherwise it would mean replacing all your Switches for Checkboxes or building an entirely different experience just for a bulk/batch interactions.