Add typehints to ImageInterface and adjust the tests

Seems like all tests are passed.

This looks good but my concern is for backwards compatibility. But may not be an issue.

Yeah, there are definitely BC concerns here - if someone else has implemented ImageInterface without return types, adding the return types here will break their code. We don't have a good plan for solving this at present except by perhaps using Symfony's debug class loader to notify downstream users of our code.

@longwave,

Thanks for the review. In this case, does it make sense to postpone this task for now and add to-dos or comments for the functions to add typehints later on? During some major changes later.

Because, for now, it looks like it's hard to continue with that task.

I moved the task to the "Active" for further discussion about what to do here.

The top level meta for this is 🌱 [Meta] Implement strict typing in existing code Active , adding this as a child and postponing. It is likely that we will do wider changes than interface-by-interface, but until we decide this issue can stay postponed.