fix(list): make dense and normal showcase responsive.

[devversion]

Currently the dense / normal demo won't shrink on mobile screen sizes.
After this commit, the two showcases will wrap on a small screen size.

Also notice, the divider is now splitting the toolbar too, instead of only the content.

FYI:

The diff is really unclear, so I just mention it here, just made the demo root-container using a row layout when bigger than breakpoint -sm, otherwise it uses a column layout.
Created two containers, which flexes to 50% on gt-smdevices, otherwise 100%
So now every container (two containers) contains now one toolbar and the associated content (normal and dense)

[ThomasBurleson]

lgtm

[EladBezalel]

I didn't want the divider to split the toolbar too but that's nvm.

thanks. lgtm

[devversion]

@EladBezalel Yes, extra mentioned that because it was some kind of a side-effect. Just kept it, because otherwise there would be a much more complex flex layout needed. So I think it still looks fine.