Add demo that re-projects data on-the-fly

[katamartin]

• Sets up new test-leap using CMIP6 demo data
  • Fetches data and calculates zoom, translate, and bounds outside of minimaps
• Makes a few tweaks to library to support this case
  • Redefines draw method every time projection changes
  • Clears the draw buffer on every invalidation
  • Makes viewport tracking the explicit responsibility of Raster
    • Avoids usage of stale context values read in draw calls
    • Relies on temporary setTimeout hack to workaround stale draws when multiple projection-related props are updated at once (aspect and other props in this case)