Add isPRCommit404 detection

[FloEdelmann]

Extracted from refined-github/refined-github#3233.

[fregante]

🎉

[fregante]

https://github.com/fregante/github-url-detection/releases/tag/v1.2.2

Also if you see any others that can be moved out of RGH let me know or send a PR (as long as the conditions aren't super specific like for is single html file or has breadcrumb)

Better to just suggest them here first just in case.

[FloEdelmann]

It seems like all custom includes/excludes we currently have in RGH don't make sense here (I've searched for the regex (in|ex)clude: \[\n\t\t\():

source/features/comments-time-machine-links.tsx:
  120: 	exclude: [
  121: 		() => !new URLSearchParams(location.search).has('rgh-link-date')

source/features/first-published-tag-for-merged-pr.tsx:
  57: 	exclude: [
  58: 		() => !select.exists('#partial-discussion-header [title="Status: Merged"]')

source/features/fork-source-link-same-view.tsx:
  32: 	exclude: [
  33: 		() => !pageDetect.isForkedRepo(),

source/features/preserve-whitespace-option-in-nav.tsx:
  22: 	exclude: [
  23: 		() => new URLSearchParams(location.search).get('w') !== '1'

source/features/quick-mention.tsx:
  58: 	exclude: [
  59: 		() => select.exists('.conversation-limited') // Discussion is locked

source/features/repo-wide-file-finder.tsx:
  30: 	exclude: [
  31: 		() => select.exists('[data-hotkey="t"]')

source/features/show-associated-branch-prs-on-fork.tsx:
  114: 	exclude: [
  115: 		() => !pageDetect.isForkedRepo()

source/features/show-open-prs-of-forks.tsx:
   96: 	exclude: [
   97: 		() => !pageDetect.isForkedRepo()
  105: 	exclude: [
  106: 		() => !pageDetect.isForkedRepo()

source/features/view-markdown-source.tsx:
  112: 	exclude: [
  113: 		() => !select.exists('.blob .markdown-body')

[fregante]

Thanks for checking!