LOD, "cartographic rendering", split screen & full-screen minimap

[Indy2222]

Design and implement support for different rendering modes & LOD based on area visible by the/a camera. For example: full 3D -> LOD / simplified 3D -> "cartographic" (mini map style)

Once this is implemented, mini map can be just a fully zoomed out orthographic camera rendered to a texture displayed in the UI.

This would enable some other nice features:

• the ability to have multiple mini maps partially zoomed in on the player's areas of interest
• split screen -> managing in parallel different parts of the map (e.g. a battle at a distant part of the map and the base town)

[github-actions]

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