Buttons no longer provide a visual cue as to whether they are internal (immersive) or external (pop-out)

Raised as a follow up to #4247

Now that the Dashboard and Editor buttons have been commonised throughout the application, we no longer get visual cues as to whether a link is a external (popout) or internal (immersive)

> V4.0.2 Node-RED shows the "Editor" button without link-out icon (to signify it is an internal link / immersive)
> Older NR versions that do not support immersive editor have the link-out icon.
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This task is to devise a means of providing visual a visual cue that informs users of popout/immersive behaviour for buttons:
- [ ] Dashboard
- [ ] Editor

Start with the follow-up issue #4247 and inspect how the Dashboard and Editor buttons are commonised throughout the application. Compare the V4.0.2 and older Node-RED examples in the issue; done means both buttons visibly communicate whether they open an immersive internal view or a pop-out.

Written by the indexing model from the issue text.