Breaking: #101392 - getIdentifier() and setIdentifier() from AbstractFile removed

See forge#101392

Description

When using the PHP API of File Abstraction Layer, there are several classes involved representing a File Object.

Next to the FileInterface there is also the AbstractFile class, where most classes extend from when representing a File.

However, in order to ensure proper code strictness, the Abstract class does not implement the methods getIdentifier() and setIdentifier() anymore, as this is indeed part of the subclasses' job.

They are now implemented in the respective classes inheriting from AbstractFile.

Impact

In an unlikely case that the TYPO3's File Abstraction Layer is extended by adding custom PHP classes extending from AbstractFile, this will result in a fatal PHP error, as the new abstract methods getIdentifier() and setIdentifier() are not implemented.

Affected installations

TYPO3 installations with a custom File Abstraction Layer code extending the actual file abstraction layer, which is highly unlikely.

Migration

Implement the two methods getIdentifier() and setIdentifier() in the custom File class extending AbstractFile.

This can also be done in previous TYPO3 versions to make the code ready for multiple TYPO3 versions.