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/ScriptableRenderContext.cs

@@ -101,6 +101,8 @@ namespace XCEngine.Rendering
             RendererListDesc rendererListDesc,
             DrawingSettings drawingSettings)
         {
+            RenderStateBlock renderStateBlock =
+                drawingSettings.renderStateBlock;
             return InternalCalls
                 .Rendering_ScriptableRenderContext_DrawRenderersByDesc(
                     m_nativeHandle,
@@ -109,7 +111,8 @@ namespace XCEngine.Rendering
                     drawingSettings.overrideMaterialPath ??
                         string.Empty,
                     drawingSettings.shaderPassName ??
-                        string.Empty);
+                        string.Empty,
+                    ref renderStateBlock);
         }
 
         public bool RecordOpaqueScenePhase()