Show viewports using a theme in global theme list

Description

If a lot of themes and viewports exist it is very cumbersome to find the themes that are actually in use. While the viewport list shows the used theme, one would need to manually match both lists in order to find unused themes.
We should add a way to see the themes that are still being used.

Environment

None
Fixed

Assignee

Unassigned

Reporter

Sync User [K15t]

Labels

None

Participants

None

QA Status

None

Deployment

None

Documentation Status

None

UI Concept

None

External Votes

None

Components

Fix versions

Configure