Deprecation: #83976 - Moved file extension detection to FAL driver
See forge#83976
Description
The only object that is allowed to handle the physical file in the FAL is the driver, as it is the only instance that knows how to access the file.
The definition of the FAL driver method 
        get is enhanced with the return
value extension.
Impact
Installations with a FAL driver 
        get method that doesn't return the
extension value will trigger a PHP 
        E_ error.
Affected Installations
Installations with 3rd party FAL drivers.
Migration
Adjust the 
        get method of your file drivers to return the extension value.