[Design] Visual foundation and rudimentary Design System

Why we do this?

As a part of new concept of Qt Creator we will also need to update Qt Creators UI visually to more professional and modern appearance and also make our usability better in component level. At this point it's essential to start building more structured design libraries and rudimentary design system to make it more effortless to design new features in the future. 

Visual foundation and design system includes:

• Study existing Qt Creator visual design and components usability
• Visual foundation for coherent user experience 
• Study and plan motion design for more intuitive user experience
• Plan the structure for design system in Figma
• Design UI components and libraries in Figma