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

[Steve-Mcl]

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.

This task is to devise a means of providing visual a visual cue that informs users of popout/immersive behaviour for buttons:

• [ ] Dashboard
• [ ] Editor