OpenGL: Light3D Shadow Blur property is ignored

[Calinou]

Godot version

4.2.dev fbe611e

System information

Fedora 38, GeForce RTX 4090 (NVIDIA 535.104.05)

Issue description

Light3D Shadow Blur property is ignored when using the Compatibility rendering method, even though it works in Forward+ and Mobile.

While Compatibility uses a cheaper PCF approach to shadowmap filtering, it is possible to make the amount of blurring adjusable as shown in #60243. This won't be as good-looking as in Forward+/Mobile, but I feel it's worth offering to make visuals more consistent when you switch rendering methods (especially if it's an automatic fallback, or for static lights that cast shadows onto dynamic objects).

Steps to reproduce

• Add some meshes in a scene.
• Add a DirectionalLight3D node and enable shadows on it.
• Try to change the Shadow > Blur property in DirectionalLight3D.

Minimal reproduction project

test_shadow_compatibility.zip