Update favicon links in head

[jayhesselberth]

Based on breaking changes from https://realfavicongenerator.net/

Fixes #2801

[jayhesselberth]

I think this is correct, based on this page.

Can someone please kick the tires?

[github-actions]

🚀 Deployed on https://671c0d339cfbdfdb6da19660--pkgdown-dev.netlify.app

[hadley]

1. Do we need to link to the .svg favicon too?
2. Would we get a better svg favicon if we switch to a svg logo? (I'm not sure if there are other concerns with that)
3. Did you have to delete the older files manually or does build_favicon() already handle that?

[jayhesselberth]

Maybe this is a good reference for what we need to include to "modernize" our approach.

[jayhesselberth]

@hadley I added the svg icons in the head, seems like the modern way. I would imagine you'd get a better SVG favicon if you started with an SVG. And I deleted the favicons manually, build_favicons() doens't handle that.

Do you have an SVG version of the logo to test?

[jayhesselberth]

The favicon checker reports some issues with the netlify deploy link (https://671c0d339cfbdfdb6da19660--pkgdown-dev.netlify.app/dev/)

There are issues with the site manifest, but more concerningly it says the SVG and ICO favicons are unavailable, despite being available and in the same place as the PNG favicon.

This might have something to do with a leading slash, which we do not include, but is included on the realfavicongenerator.net itself. Pasting realfavicongenerator.net into the checker, it looks like everything passes.

This could also be caused by the dev site URL, wondering if the paths on a dev site should be relative to "/dev".