If an entity is in a workspace, the `workspace` field is not exported

Problem/Motivation

If you're using Workspaces, an entity's workspace field will not be exported. This kind of sucks, because it's impossible to export a set of content in a workspace, or across a set of workspaces.

The reason the field is skipped is because the workspace field is internal, and \Drupal\Core\TypedData\TypedDataInternalPropertiesHelper::getNonInternalProperties() specifically skips internal properties.

Proposed resolution

Consider making a special exception for the workspace field, and allow it to be exported despite being internal.