Use `super` instead of `platform_impl::platform` in paths

[madsmtm]

Makes it easier to do refactors later on

[kchibisov]

Honestly, I really don't like super path for modules. It's not that clear where things are coming from, etc. They are not that readable and prone to errors when you move files around (e.g. when you move something to a module).

[madsmtm]

I agree somewhat, for example I didn't change this on the wayland platform, since it would mean doing super::super::super. But I think crate::platform_impl::platform is just ugly and confusing (since there's not actually a platform module in platform_impl, it's just an implementation detail of how platform_impl works).

Motivation was because I'd like to change these paths in the future, and it would mean a smaller diff when that time comes.

[kchibisov]

I don't like super in general.