Rollup merge of #102799 - rol1510:issue-100421-fix, r=notriddle

rustdoc: remove hover gap in file picker

Fixes #100421

Before:
<img width="385" alt="image" src="https://user-images.githubusercontent.com/29011024/194677087-fda2db3e-126d-47cf-8152-c554e3c25a54.png">

After:
<img width="388" alt="image" src="https://user-images.githubusercontent.com/29011024/194676774-7a50ace9-4060-492e-849a-ad85d9132630.png">

longe module names also wrap nicely:
<img width="389" alt="image" src="https://user-images.githubusercontent.com/29011024/194678516-f2497b3a-8d50-439b-9d69-3fa9fb43b84d.png">

Also if you zoom out very far, the arrows did move to the left, in relation to the text below. This is now also fixed.
<img width="818" alt="image" src="https://user-images.githubusercontent.com/29011024/194677652-cfdf129d-f5db-4f26-ac3c-3d0853e89619.png">

CSS doesn't have a lot of controll over the `::marker` element, so now the `::after` element is used to draw the arrows.

Now the whole line is clickable wihtout gaps.

Author: JohnTitor