Use higher shadow filtering quality settings in 3D demos (#1067)
The 3D demos aren't very demanding and Godot has been optimized
a bit since 4.0's release, so we can afford using higher quality
shadow settings for less noisy shadow filtering.
This also tweaks shadow bias to reduce shadow acne in the Voxel demo.
The time slider in the Physical Light and Camera units demo now
allows for more precise adjustments.