Breaking: #76802 - Drop xcache cache backend

See Issue #76802

Description

The xcache core cache backend has been dropped because PHP7 does no longer support xcache.

Impact

Instances will throw an exception or a fatal error using a cache with this backend configured.

Affected Installations

Instances that still use a configuration in LocalConfiguration.php or AdditionalConfiguration.php like:

'SYS' => [
    'caching' => [
        'cacheConfigurations' => [
            'aCache' => [
                'backend' => 'TYPO3\\CMS\\Core\\Cache\\Backend\\XcacheBackend',

Migration

Affected instances must switch to a different cache backend, APCU PHP module with ApcuBackend provides the same local server in memory characteristics like xcache and should be considered as alternative.