Arrange tiles in 2D in the tileset view

[dacap]

From #977 (related to #1575 in some way) we want to add an option to arrange tiles in a 2D map. The tileset view/palette is linear, but we should be able to see a 2D arrange of them (a tilemap). We can have two options above/at the side of the tileset view to switch between both modes.

This 2D view should fix these problems:

• [ ] https://github.com/aseprite/aseprite/issues/3179
• [ ] https://github.com/aseprite/aseprite/issues/3179#issuecomment-1044863435
• [ ] https://github.com/aseprite/aseprite/issues/4471