Make the Default Avatar support Gravatar's newly added Initials Avatars and Color Avatars

[haozi]

Gravatar added Initials Avatars and Color Avatars last month, and I thought we could integrate them into WordPress. Like the other default avatar types.

Gravatar blog post: ​https://blog.gravatar.com/2025/02/19/initials-avatars-email-signatures/
Gravatar API documentation: ​https://docs.gravatar.com/api/avatars/images/

[haozi]

Here:

Trac ticket: https://core.trac.wordpress.org/ticket/63087

Good job, I can test it in playground.

[audrasjb]

Previously: #57493

Working fine on playground

Also tested on Playground with version 6.8-beta2.

Steps done:

• Settings > Discussion > Default Avatar > "Initials (Generated)" and "Colors (Generated)" available
• Users > Profile > Profile Picture is updated

Working as expected ✅

[audrasjb]

In 60269:

Users: Add support for Initials and Color Gravatar images in default user profile pics.

Gravatar includes support for Initials and Color auto-generated images. This changeset adds them to the built-in feature for user profile images.

Props haozi, audrasjb, getsyash, valentingrenier.
Fixes #63087.
See #57493.

[SergeyBiryukov]

In 60897:

Coding Standards: Simplify the initials avatar type handling in get_avatar_data().

Includes:

• Converting a long ternary to an if/elseif block for better readability.
• Reusing an existing translatable string for user's first name and last name.
• Replacing empty() checks with more specific checks for an empty string.
• Replacing is_object() check with a check for a WP_Comment instance.

Follow-up to [53501], [60269].

See #63087.

[TobiasBg]

@SergeyBiryukov: The false === strpos( $name, ' ' ) in [60897] could be made more readable with ! str_contains( $name, ' ' ), I think?

[SergeyBiryukov]

Replying to TobiasBg:

The false === strpos( $name, ' ' ) in [60897] could be made more readable with ! str_contains( $name, ' ' ), I think?

Ah yes, thanks :)

[SergeyBiryukov]

In 60900:

Code Modernization: Use str_contains() in get_avatar_data().

str_contains() was introduced in PHP 8.0 to perform a case-sensitive check indicating if the string to search in (haystack) contains the given substring (needle).

WordPress core includes a polyfill for str_contains() on PHP < 8.0 as of WordPress 5.9.

Follow-up to [52039], [55988], [56245], [60897].

Props TobiasBg.
See #63087.