Breaking: #107871 - Remove backend avatar provider registration via $GLOBALS 

See forge#107871

Description 

Registering backend avatar providers via $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['backend']['avatarProviders'] has been replaced by autoconfiguration using the backend.avatar_provider service tag. This tag is added automatically when the PHP attribute #[AsAvatarProvider] is applied. Manual configuration in Services.yaml is still possible, particularly if autoconfiguration is disabled.

Impact 

Using the $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['backend']['avatarProviders'] array has no effect in TYPO3 v14.0 and later.

Affected installations 

All installations that use $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['backend']['avatarProviders'] to register backend avatar providers are affected. This registration is typically performed in an ext_localconf.php file. The extension scanner will report any such usages.

Migration 

Migrate existing registrations to the new autoconfiguration-based approach.

Before:

EXT:my_extension/ext_localconf.php 
use MyVendor\MyExtension\Backend\Avatar\MyAvatarProvider;

$GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['backend']
    ['avatarProviders']['my_provider'] = [
        'provider' => MyAvatarProvider::class,
        'before' => ['provider-1'],
        'after' => ['provider-2'],
    ];
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After:

EXT:my_extension/Classes/Backend/Avatar/MyAvatarProvider.php 
use TYPO3\CMS\Backend\Attribute\AsAvatarProvider;
use TYPO3\CMS\Backend\Backend\Avatar\AvatarProviderInterface;

#[AsAvatarProvider(
    'my_provider',
    before: ['provider-1'],
    after: ['provider-2']
)]
final class MyAvatarProvider implements AvatarProviderInterface
{
    // ...
}
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If you need to support multiple TYPO3 Core versions simultaneously, ensure that both registration methods are implemented: the legacy $GLOBALS based registration as well as the new tag-based approach.