Auto merge of #84834 - GuillaumeGomez:sidebar-unification, r=jsha

Auto merge of #84834 - GuillaumeGomez:sidebar-unification, r=jsha

Sidebar unification

This PR does a few things:
 * Put crates list at all levels (before, it was only on the "top" items)
 * Fix bug in module sidebar: the list of items was from the parent module.

The other changes (on bootstrap mostly) were to allow to generate multiple crates in a same folder so that we can ensure that clicking on the crates in the sidebar works as expected.

I added a rustdoc-gui test to ensure everything is where it should be.

r? `@jyn514`