Add "Robohash" support for avatar_default

[juliobox]

Hello

Since Gravatar is officially handling RoboHash as avatars, we should add it to WordPress.

Source: ​https://en.gravatar.com/site/implement/images/
Test: add_filter( 'pre_option_avatar_default', function() { return 'robohash'; } );
File: ​https://github.com/WordPress/wordpress-develop/blob/trunk/src/wp-admin/options-discussion.php#L276
Patch: 'robohash' => __( 'RoboHash (Generated)' ),
Github PR:
Thanks for reading.

Add support for "RoboHash" avatars for Gravatar
This is a native option, source: ​https://en.gravatar.com/site/implement/images/

Trac ticket: https://core.trac.wordpress.org/ticket/57493#ticket

[audrasjb]

Thanks for the ticket and patch!

I added a commit to your PR to remove an unwanted whitespace for better WPCS compliance :)

[audrasjb]

Works fine on the admin screen

[audrasjb]

Works fine on front-end when robohash is selected as default avatar option

[audrasjb]

Moving for 6.2 consideration.

[audrasjb]

Self assigning for commit.

[audrasjb]

Note:
This HelpHub page needs to be updated: ​https://wordpress.org/support/article/settings-discussion-screen/#avatars

[audrasjb]

In 55238:

Users: Add support for RoboHash Gravatar images in default user profile pics.

Gravatar includes support for RoboHash auto-generated images. This changeset adds it to the built-in feature for user profile images.

See Gravatar docs: ​https://en.gravatar.com/site/implement/images/.

Props juliobox, audrasjb.
Fixes #57493.

[audrasjb]

Reopening to address a follow-up commit: I noticed we also need to update two function docblocks. Follow-up commit incoming.

[audrasjb]

In 55239:

Users: Update get_avatar_url() and get_avatar() to include RoboHash support.

Follow-up to [55238].

Fixes #57493.

Committed in https://core.trac.wordpress.org/changeset/55238