Problem/Motivation
Came up as a test fail as part of #2976394: Investigate problems with Symfony 4 now but it is not technically a Symfony 4 fail, since the implemented methods were already internal in Symfony 3.4. It looks as though this interface was not meant to be implemented as it explicitly says some of its methods are not to be considered stable.
Proposed resolution
Ultimately looks like we need to get off of this interface. We can add the fail to our deprecation listener to work around the notices for now since we need to keep backwards compatibility.
Remaining tasks
Discuss.
User interface changes
None.
API changes
None.
Data model changes
None.
Release notes snippet
N/A