Improve VS Code design resources in Figma

[kkbrooks]

Our Figma library is out of date, lacks documentation, and we've received feedback that its difficult for extension teams to use when designing their experience.

Areas to improve

• [x] Add variables for spacing and corner radius
• [ ] Remove outdated color styles
• [ ] Rebuild controls with up-to-date features (auto layout, modes, etc)
  • [ ] Activity Bar
  • [ ] Chat
  • [ ] Dialogs
  • [ ] Editor
  • [ ] Extensions
  • [ ] Hovers
  • [ ] Input
  • [ ] Labels
  • [ ] List
  • [ ] Menu
  • [ ] Notebooks
  • [ ] Notifications
  • [ ] Peek Views
  • [ ] Panel
  • [ ] Progress
  • [ ] Quick Pick
  • [ ] Settings
  • [ ] Sidebar
  • [ ] Status bar
  • [ ] Suggest Widget
  • [ ] Tabs
  • [ ] Templates
  • [ ] Titlebar
  • [ ] Utilities
• [ ] Add relevant links to API documentation to each applicable control
• [ ] Redo Type, Colors, Icon page
• [ ] Redo README/intro page
• [ ] Republish to the community as a UI Kit