Allow to edit external tile maps during runtime

[D8H]

• Add a tile map capability
• Add a collision mask directly in the external tile map object (additional collision masks can still be added with the tile map collision mask object)
  • The collision mask "class" can be left empty (but there won't be default full tile hit-box since we can't tell between empty and full)

Demo

• Add an example with a simple tile map editor GDevelopApp/GDevelop-examples#1020