Various terrain improvements: (#3942)

* Various terrain improvements:
- Height now stored in a R16_unorm to decrease the amount of memory / memory bandwidth needed for the height field
- Many simplifications to the feature processor
- Added a shader to render to the depth pre pass
- Pulled common functionality needed by depth and forward to a common include shader
- Forward shader now outputs to all the expected render targets
- Adjusted the way normals and lighting are being calculated

Signed-off-by: Ken Pruiksma <pruiksma@amazon.com>

* Adding missing shader files. Updated terrain shader to alter the color slightly with height.

Signed-off-by: Ken Pruiksma <pruiksma@amazon.com>

* Removed pixel shader code from terrain depth pass

Signed-off-by: Ken Pruiksma <pruiksma@amazon.com>

* Renamed the depth pass shaders to no longer indicate they include a pixel shader.

Signed-off-by: Ken Pruiksma <pruiksma@amazon.com>

* Removing unneeded code from TerrainCommon.azsli

Signed-off-by: Ken Pruiksma <pruiksma@amazon.com>

Code/Editor/Include/ObjectEvent.h

@@ -27,7 +27,6 @@ enum ObjectEvent
     EVENT_OUTOFGAME,        //!< Signals that editor is switching out of the game mode.
     EVENT_REFRESH,          //!< Signals that editor is refreshing level.
     EVENT_DBLCLICK,         //!< Signals that object have been double clicked.
-    EVENT_KEEP_HEIGHT,  //!< Signals that object must preserve its height over changed terrain.
     EVENT_RELOAD_ENTITY,//!< Signals that entities scripts must be reloaded.
     EVENT_RELOAD_GEOM,  //!< Signals that all possible geometries should be reloaded.
     EVENT_UNLOAD_GEOM,  //!< Signals that all possible geometries should be unloaded.