Only display icons for navigation group of menus

[rebornix]

re #27467

For commands in navigation group, right now we'll try to show icons first if they exist. If not, we display the command title. Our builtin explorer title only shows icons, so maybe we should only allow icons to be displayed as well. Allowing text being displayed sometimes looks weird.

[sandy081]

Its a good point. These actions are contributable. Have to see how they are rendered in other locations.

@bpasero What do we do in editor title area?

[bpasero]

The SCM viewlet has a similar "issue" where I would like to see an icon and not the text:

I think today we are not restricting any extension to force use an icon, in other words labels are allowed if no icon is provided. @jrieken would know for sure if that is true.

[jrieken]

Yes, not restrictions and I'd that's fair. Tho it should not look ugly if no icons are provided, e.g no spacing issues like above.