Rollup merge of #103650 - notriddle:notriddle/line-anchors, r=GuillaumeGomez

rustdoc: change `.src-line-numbers > span` to `.src-line-numbers > a`

Example: https://notriddle.com/notriddle-rustdoc-demos/line-anchors/test_dingus/fn.test.html

This allows people to treat them like real links, such as right-click to copy URL, and makes the line numbers in a scraped example work at all, when before this commit was added, they had the clickable pointer cursor but did not actually do anything when clicked.

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

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

diff --cc src/test/rustdoc-gui/source-code-page.goml
Simple merge