`CesiumDefaultTilesetMaterial` not receiving proper directional lighting at certain angles

This might be an issue with the shader itself. As you can see below, lighting and shadows from a directional light are not properly received by the material at certain angles.

We are trying to a do a day and night cycle based on time, date and location so we are utilizing a wide range of rotations from a single directional light as if it is a real world sun light.

| **X > 140°** | **X < 140°** |
|--------------|---------------|
|||

*Note: "X" represents the angle value at X-Axis of rotation. Y and Z rotations on the preview is set to zero for simplicity.*

Reproduce the issue with CesiumDefaultTilesetMaterial using a directional light and the X-axis rotations described in the report, comparing values above and below 140 degrees. Inspect the material's shader and verify that directional lighting and shadows are received consistently across the tested angles.

Written by the indexing model from the issue text.