Rustdoc responsive design makes suboptimal tradeoffs, especially on tall windows

[the8472]

When displaying IDE and a browser showing rustdocs side by side I can easily end up with a 800x1400 viewport. At that resolution the sidebar takes up a large fraction of the space, forcing unnecessary linebreaks.

At lower widths (<700px) media queries use a different layout without the sidebar, but that also has problems. For one it hides the [-] toggle on the top right which I like to use to get a more compact overview due to the lack of method indexes (#40273). Secondly, it mostly removes the sidebar's content. With enough vertical screen estate it might make more sense to just move it to the top or bottom.

[GuillaumeGomez]

The UI has been greatly reworked, preventing this issue from happening anymore. I'm closing it but if you still have some issues around the "responsiveness", please reopen it.