[Feature Request] Add support for distance field shadows on Single Layer Water shading model

Add support for distance field shadows on Single Layer Water shading model

(report of it missing in Fortnite here: https://jira.it.epicgames.net/browse/FORT-217878)

1. Open QA-WaterWork
2. Set directional light cascade count to 1 and distance to 2000
3. You should see the shadow disappear on water and ground after that distance.
4. Enable DistanceField shadow on that light and set as larger distance. Shadow from traced distance field should appear on both water and terrain. (before, it was not appearing on water).