Rollup merge of #56874 - JohnHeitmann:docs-spacing, r=GuillaumeGomez

Simplify foreign type rendering.

Simplified foreign type rendering by switching from tables to flexbox. Also, removed some seemingly extraneous elements like “ghost” spans.

Reduces element count on the `std::iter::Iterator` page by 30%. On my laptop it drops Iterator page load time from ~15s to ~10s. Frame times during scrolling are a hair lower too.

Known visual changes (happy to tweak based on feedback):
* The main `impl ...` headers are now getting the default, larger, h3 font size. This was an accident, but I liked how it turned out so I didn't fix it.
* There's a hair less vertical spacing between the end of a where block and the start of the next fn. Now, all spacing is consistent. I think this looks a bit worse. I may tweak vertical spacing more here or in a follow-up that cleans up vertical spacing more broadly.
* "[src]" links are all sized at 17px. A few were 19px in the original.

I haven't yet done heavy cross-browser or cross-crate testing. I was hoping to get a quick thumbs up or thumbs down here at this first draft, then if this is on the right track I'll spend some time on that testing.

TODO:

- [x] Test on Chrome
- [x] Test on Firefox
- [ ] ~~Test on UC Android~~
- [x] Test on Edge
- [x] Test on iOS safari
- [x] Test on desktop safari
- [x] Update automated tests
- [x] Increase vertical margin
- [x] Fix "Important traits for" hover overlap
- [x] Wait for #55798 to land & merge it

0 files changed, 0 insertions, 0 deletions