Derive HighContrast from Adwaita
Right now, HC is a completely separate 'theme'. This has historical reasons of using fullcolor icons for the main theme with low contrast.
The purpose of the HC theme is not to increase the target sizes, but to... increase contrast. The biggest issue with HC is how little testing it gets. I don't mean when designing the theme itself but apps getting tested with it. I suggest for gtk4 we:
- Make it easier for app developers to test against HC, making it more exposed in the gtk inspector/Builder
- Reuse 99% of Adwaita. It's about increased contrast now that we use symbolic icons, the reason to maintain a separate theme is minimal. This is what the mac does IIRC.