Draft: Check if terminal capable of rendering unicode

What does this Merge Request do and why?

This MR fixes an issue where 'icons' (emojis) were not rendering properly in some terminals (e.g. Docker), e.g.

Before

After

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.