Make the "softness" of soft shadows adjustible per-light. (#1454)

Note: Thanks to the nature of YAML properties in RobustToolbox, this commit is only an API blocker if the Softness property is directly manipulated from code, which is unlikely.

Resources/Shaders/Internal/light-soft.swsl

@@ -13,7 +13,7 @@ highp float createOcclusion(highp vec2 diff)
     // Change soft shadow size based on distance from primary occluder.
     highp float distRatio = (ourDist - occlDist.x) / occlDist.x / 2.0;
 
-    perpendicular *= distRatio;
+    perpendicular *= distRatio * lightSoftness;
 
     // Totally not hacky PCF on top of VSM.
     highp float occlusion = smoothstep(0.1, 1.0, ChebyshevUpperBound(occlDist, ourDist));

Resources/Shaders/Internal/light_shared.swsl

@@ -13,6 +13,7 @@ uniform highp vec4 lightColor;
 uniform highp vec2 lightCenter;
 uniform highp float lightRange;
 uniform highp float lightPower;
+uniform highp float lightSoftness;
 uniform highp float lightIndex;
 uniform sampler2D shadowMap;