Off-screen windows should be more obvious when shown

When testing #7752, the following observation was noted:

> I think there should be some type of indication that something was rendered off-screen. The whole MDI canvas is very bad user experience (yet we're stuck with it for now) and clicking a button that reveals a window should reveal that window. Perhaps we move the viewport to bring it to focus?

Another idea is to show some type of arrow/hint that new content is visible.

### Implementation Details / Mockup

TBD

Related: #7595

Start by reviewing the observations in #7752 and the related issue #7595, then inspect how the MDI canvas reveals windows that were rendered off-screen. The issue needs a decided approach and mockup before implementation; done should mean newly revealed off-screen content is clearly indicated or brought into view.

Written by the indexing model from the issue text.