How to add an additional file validator

Problem/Motivation

I was wondering if there is a recommended technique for a contrib module to add an additional validator to the file entity browser upload widget.

I already have this functionality working with core file and image fields, by adding the validator to the #upload_validators array when #type === 'managed_file', and would like to get this working for sites that use entity browser as well.

I tried adding my validator to $element['entity_browser']['#widget_context']['upload_validators'] but this didn't seem to work with file entity browser's dropzone upload widget.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes