EVSM improvements (#9758)

- refactoring/clecanup to make some changes easier
- VSM mipmap generation was mistakenly disable when blur radius was 0
- analytic variance was disabled because the math only worked for VSM. Fixed the math.
- better handling of large blurs when using fp32
- implement EVSM equivalent of receiver plane normal bias
- use correct EVSM clearing color
- mipmapping with point lights works much better (no seams)
- min variance is computed automatically
- custom high precision mipmaping shader for VSM

android/filament-android/src/main/java/com/google/android/filament/View.java

@@ -2121,7 +2121,7 @@ public class View {
          */
         public boolean highPrecision = false;
         /**
-         * VSM minimum variance scale, must be positive.
+         * @deprecated has no effect.
          */
         public float minVarianceScale = 0.5f;
         /**