Add JavaScript-based redirects to supplement Read the Docs redirects

[Calinou]

Read the Docs has an upper limit on the number of redirects that canapply. This limit is exceeded by the current redirects.csv,which means many redirects don't apply correctly.

While this JavaScript-based solution is not as seamless from the user's perspective, it has no limit on how many redirects can be defined.

To test this PR, build the website locally and run simple-http-server --try-file 404.html in _build/html. It's important to instruct the local web server to use 404.html as a custom 404 page, or you won't be able to test this.

Note that redirects.csv isn't modified by this PR yet, so this won't perform all redirects from the previous contributing section to contributing.godotengine.org.

We'll also probably want to change the redirects CSV URL to match the current branch in the long run. I'm not sure how we should do this in a way that keeps working with local web servers (which may not have /latest, /stable or /4.5 in the URL). Maybe we should just modify custom.js for each branch?

[Ivorforce]

Note that redirects.csv isn't modified by this PR yet, so this won't perform all redirects from the previous contributing section to contributing.godotengine.org.

This is addressed in #11315.

We'll also probably want to change the redirects CSV URL to match the current branch in the long run. I'm not sure how we should do this in a way that keeps working with local web servers (which may not have /latest, /stable or /4.5 in the URL). Maybe we should just modify custom.js for each branch?

I think the easiest solution might be to place redirects.csv in the public folder, and simply grab it by using the base url + /redirects.csv.

[Calinou]

I think the easiest solution might be to place redirects.csv in the public folder, and simply grab it by using the base url + /redirects.csv.

Wouldn't that break RTD redirects though? We still want them to work when possible to reduce the reliance on JavaScript, as it's less optimal.

Edit: Nevermind, this is handled by https://github.com/godotengine/godot-docs/blob/master/_tools/redirects/create_redirects.py rather than CSV file itself.

Edit 2: Done. The redirects CSV is now in _static and is loaded directly, so it also works using the local redirects.csv during local testing. I've also rebased the PR on top of #11315.

[Ivorforce]

Awesome! Does that leave the PR in a reviewable / potentially mergable state?

[Calinou]

I've added support for redirecting to absolute URLs. Note that the existing redirects.csv has some typos which I didn't notice while reviewing #11315 (search for instances of //architecture). Should I fix them in this PR, or should you open a new PR?

[Ivorforce]

I've added support for redirecting to absolute URLs. Note that the existing redirects.csv has some typos which I didn't notice while reviewing #11315 (search for instances of //architecture). Should I fix them in this PR, or should you open a new PR?

Ah, dang, sorry. I think it's fine to add them here.

[Calinou]

Ah, dang, sorry. I think it's fine to add them here.

Done 🙂

[mhilbrunner]

Looks good to me. Would be good to add a comment to create_redirects.py that it is now obsolete, pointing to custom.js instead.

Will test this a bit.

[mhilbrunner]

Alright, lets try this. Thanks both of you! We'll see how this goes.

[mhilbrunner]

Cherrypicked to 4.5 in #11448.