Breaking: #102971 - Most classes of EXT:workspaces declared internal

See forge#102971

Description

A few additional classes of extension "workspaces" have been declared @internal. With this, most of the classes are now considered internal handling, except, of course, dispatched events.

Impact

Extensions extending or using workspace classes as PHP API that are now marked @internal may break, when the Core changes such classes. This will not be considered breaking.

Affected installations

Few extensions extend workspaces as such, and the backend workspaces application in particular.

Migration

Extension authors who need to extend from classes within EXT:workspaces should reconsider on why this needs to be done. They should expect these may break without further notice.

Legit use cases can often be moved towards some additional event instead. Extension authors are encouraged to come up with specific solutions in those cases.