Implement vertical exaggeration of 3D Tiles in 2D and Columbus View modes

[jjhembd]

Feature

#11655 enabled vertical exaggeration of 3D Tiles. However, the current shader-based implementation only works in SceneMode.SCENE3D.

To make it work in SceneMode.SCENE2D and SceneMode.COLUMBUS_VIEW, the curvature term czm_eyeEllipsoidCurvature will need to be set to zero. This will require some changes in VerticalExaggerationStageVS to avoid division by zero. Additionally, czm_eyeHeight will need to be investigated to verify it is still valid in 2D modes; otherwise, VerticalExaggerationStageVS can transition between czm_eyeHeight and czm_eyeHeight2D