Make checkbox UI consistent

[domoritz]

Describe the bug
Different checkboxes use various styles. They should all use native UI elements instead.

I didn't even realize that I could check the circle for quite a while. I think this will trip up many first time users and should therefore be fixed.

Screenshots

[aaronraimist]

Do you have a screenshot of the native checkbox UI you are expecting? I agree the unchecked circle isn't very visually helpful as to what it is but as far as I can tell it is essentially the same as the checkboxes as in the system apps. For example these are in the Messages app

and these are in Settings

[domoritz]

I think the circled checkboxes are quite rare. I see multi selects with submenus a lot more often. For example, in the rest of the notification setting ui.

[ShadowJonathan]

I think the rounded checkboxes need extra context before they can be used as such, for example, these are presented in context of other objects, which themselves then lend a context to be 'selectable'.

Some extra data from #5277;

https://twitter.com/MrPseu/status/1467846022567280640

A person got stuck on the ToS screen because of this, and so i think using SwiftUI toggles for single button settings is the way forward.

[ShadowJonathan]

What's more, the following StackOverflow answer says the following RadioButton style is prevalent across iOS, and it took me a moment to actually realise thats true;