Rollup merge of #104967 - willcrichton:fix-scrape-examples, r=notriddle

Fix UI issues with Rustdoc scrape-examples feature.

A few regressions have been introduced into scrape-examples in the last few months. This commit fixes those regressions:
* Help file was being loaded from the wrong place (introduced in f9e1f6ffdf03ec33cb29e20c88fc7bcc938c7f42).
* CSS selector in JS has a typo (introduced in 14897180ae6a0506a5ad0a9f6a30ae1f75916179).
* Line numbers in scraped example code snippets are overflowing (not sure if this was ever fixed). Changing from flexbox to grid display fixed this issue.

diff --cc src/librustdoc/html/static/css/rustdoc.css
Simple merge