useful-not-found-page - Refactor

[fregante]

• part of Svelte components #9810

Test URLs

• With repo header: 404 issue: https://github.com/refined-github/refined-github/issues/888888
• With repo header: 404 file: https://github.com/refined-github/refined-github/blob/main/source/features/a-horse-with-no-name.tsx
• With repo header: 410 file: https://github.com/refined-github/refined-github/blob/main/extension/content.js
• With repo header: 404 ref: https://github.com/refined-github/refined-github/blob/eggs-for-branch/package.json
• With PR header: 410 commit: f3b5e71 (#9773)
• Raw: 404 repo: https://github.com/fregante/404-repo
• Raw: 404 user: https://github.com/__cant-find-user

Screenshot

[fregante]

Current status:

Arguably we don't need this breadcrumb, we could alter the existing path in place, linkifying the sub-parts.

We also have additional useful links outside the breadcrumbs:

[fregante]

Long overdue updates: the breadcrumbs now only appear on repo files. There are very few instances in which a breadcrumb makes sense outside of this. The only one being :real-user/:404-repo, which needs a single link and could be done separately.

[fregante]

Lost in the mess of this huge feature was this helper that crossed-through GitHub's own breadcrumbs. Sadly these only appear on /tree/ pages, so we still need our own breadcrumbs on /blob/ pages.

Selector updated, our breadcrumb hidden on /tree/ pages.

[fregante]

Wasn't me. Fails without RG too

https://github.com/refined-github/refined-github/tree/nope/source/lol/highest-rated-comment