[material-ui][ToggleButtonGroup] Add functionality to keep buttons separate

[Mikilll94]

Summary

Currently it's not possible to easily separate buttons in ToggleButtonGroup component.

If you try to do that i.e. by using CSS gap property, then as you can see left borders are missing

https://stackblitz.com/edit/react-kkov5aav?file=Demo.tsx

Examples

No response

Motivation

In Joy UI you can set spacing for buttons in ToggleButtonGroup. Material should also have this feature:

Search keywords: ToggleButtonGroup, separate

[siriwatknp]

I think the added demo is misleading, it looks like the toggle button supports spacing feature. I think it makes more sense to move it to the customization section and may be render outlined and no-outlined next to each other with minimal style customization.