* Added HasTerrain attribute for buffer overflow safety if reading terrain data before terrain has been initialized on the GPU
* Fix terrain leaking gpu buffer if disabled or deleted
Set HasTerrain flag to false once all terrains are gone
* Exposed more terrain helpers in TerrainCommon.hlsl
- GetWorldHeight
- IsInBounds
- SampleColor
* built shaders
* built terrain shader
* Changed Has() to terrainCount instead
* Make count 0 if disabling the last terrain
* built shaders
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