Forward Rendering shading flicker on some assets set to Static

When forward shading is enabled some assets will have a shadow flicker along their face geometry. It has a similar look of z-fighting with polygon faces. This issue does not happen in Deferred rendering.

Notes regarding this:

• Issue more evident on all assets when using view mode for Lightmap Density
• Asset must be set to Static mobility. Stationary and Movable do not exhibit the same issue.
• Lighting does not have to be built for the actor to see the flicker.
• Only happens in Forward Shading
• Only happens on some assets.

Tested in:
Broken: 4.14.3 -3249277
Broken: 4.15 Preview 1 CL-3258144
Broken: 4.16 Dev-Rendering CL- 3261719

1. Open attached project or import attached asset.
2. Enable Forward Shading via the project settings if it's not already enabled for the project.
3. Place imported asset in the scene and make sure it's mobility is set to static.
4. The directional light can be set to any mobility. If it's static/stationary just make sure to rebuild.

Results: Visible flickering on the mesh that is not z-fighting from mesh geometry.