Auto merge of #137229 - GuillaumeGomez:expand-macro, r=lolbinarycat

Add support for macro expansion in rustdoc source code pages

This is what it looks like:

![Screenshot From 2025-02-18 18-08-51](https://github.com/user-attachments/assets/ce2b3806-6218-47df-94bf-e9e9ed40cd41)

![image](https://github.com/user-attachments/assets/891042db-8632-4dba-9343-e28570c058fe)

You can test it [here](https://rustdoc.crud.net/imperio/macro-expansion/src/lib/lib.rs.html). In this case, I also enabled the `--generate-link-to-definition` to show that both options work well together.

Note: <del>There is a bug currently in firefox where the line numbers are not displayed correctly if they're inside the "macro expansion" span: https://bugzilla.mozilla.org/show_bug.cgi?id=1949948<del> Found a workaround around this bug.

r? `@notriddle`

Author: bors