ADD: CSM half-working

shaders/input_structures.glsl

@@ -1,12 +1,18 @@
+// Maximum number of shadow cascades supported in shaders
+#define MAX_CASCADES 4
+
 layout(set = 0, binding = 0) uniform  SceneData{
 
     mat4 view;
     mat4 proj;
     mat4 viewproj;
-    mat4 lightViewProj;
+    mat4 lightViewProj; // legacy single-shadow for fallback
     vec4 ambientColor;
     vec4 sunlightDirection; //w for sun power
     vec4 sunlightColor;
+    // CSM data
+    mat4 lightViewProjCascades[MAX_CASCADES];
+    vec4 cascadeSplitsView; // positive view-space distances of far plane per cascade
 } sceneData;
 
 layout(set = 1, binding = 0) uniform GLTFMaterialData{