feat(srp): add render state block scene draw overrides

- add managed RenderStateBlock authoring types and wire them through DrawingSettings
- let RenderObjectsRendererFeature author depth and stencil overrides for scene draws
- apply scene draw render state overrides inside builtin forward pipeline and document the stage plan

managed/XCEngine.ScriptCore/Rendering/Core/CompareFunction.cs

@@ -0,0 +1,14 @@
+namespace XCEngine.Rendering
+{
+    public enum CompareFunction : byte
+    {
+        Never = 0,
+        Less = 1,
+        Equal = 2,
+        LessEqual = 3,
+        Greater = 4,
+        NotEqual = 5,
+        GreaterEqual = 6,
+        Always = 7
+    }
+}