Add `ResponsiveScaffold` equivalent for non-drawer lists

[glacials]

Thank you for this library! It's exactly what I was looking for, and I was afraid I'd have to build a crappy version of it myself until I found this.

If I understand the documentation correctly it seems that ResponsiveScaffold solves simple use cases and requires low effort to integrate, while ResponsiveListScaffold.builder solves more use cases and requires high effort to integrate.

To find out that the former only supports drawers, not persistent lists was a surprise to me. I can integrate ResponsiveScaffold into my app easily (which is a fantastic experience!) without changing much code, but I want my "index of items" view to be a screen on phones, or a left-half / left-third part of screen on tablets (the same as the "Responsive List" in the demo). Instead it is a drawer on both.

To use the more complex ResponsiveListScaffold.builder to get the behavior I want requires complexity I'm not willing to shoot for right now, especially because I'm dealing with Iterators that would be hard to index into, so a heavy refactor would be called for.

Thanks!