Extend favicon making it a more detailed site icon

[izmeez]

Description of the need

Backdrop has inherited the favicon .ico file tradition from Drupal.

It would be really nice to see this upgraded to a proper, more detailed, shortcut icon or site icon like Wordpress uses. This was mentioned in #5661 where the idea of having them as managed files is also supported.

The Site Icon is what you see in browser tabs, bookmark bars, and can be saved on mobile home screens. WordPress supports site icons, in various graphic formats, that are square and at least 512 × 512 pixels.

I have not yet tested if browsers and mobile home screens support svg, but that would be awesome.

There are several related Backdrop issues pertaining to the favicon and logo including: overhaul the settings for favicon and logo and making them managed files (#5661); adding tokens to enhance referencing and reusing logos elsewhere (#5871); ensuring logo and favicon go into the public files even when private file-system is set (#6380); to fix the caching of favicon(#898); updating the wording on the site-information page (#2601).

Alternatives that have been considered

There is also the contrib module https://github.com/backdrop-contrib/responsive_favicons that supports png graphics at least 260 x 260 pixels. I have not yet tested this module.

Additional information

Add any other information or screenshots that would help.

Draft of feature description for Press Release (1 paragraph at most)

Backdrop now includes...