Rollup merge of #88742 - GuillaumeGomez:fix-table-in-docblocks, r=nbdd0121

Fix table in docblocks

"Overwrite" of #88702.

Instead of adding a z-index to the sidebar (which only hides the issue, doesn't fix it), I wrap `<table>` elements inside a `<div>` and limit all chidren of `.docblock` elements' width to prevent having the scrollbar on the whole doc block.

![Screenshot from 2021-09-08 15-11-24](https://user-images.githubusercontent.com/3050060/132515740-71796515-e74f-429f-ba98-2596bdbf781c.png)

Thanks `@nbdd0121` for `overflow-x: auto;`. ;)

r? `@notriddle`

diff --cc src/librustdoc/html/markdown.rs
Simple merge

diff --cc src/librustdoc/html/render/print_item.rs
Simple merge