NodeMaterial: Fix fog. (#31463)

* NodeMaterial: Fix fog.

* NodeBuilder: Clean up.

* E2E: Update screenshots.

* E2E: Update screenshot.

src/materials/nodes/NodeMaterial.js

@@ -1071,7 +1071,7 @@ class NodeMaterial extends Material {
 
 			output.assign( outputNode );
 
-			outputNode = vec4( fogNode );
+			outputNode = vec4( fogNode.toStack() );
 
 		}
 

src/nodes/core/NodeBuilder.js

@@ -196,7 +196,7 @@ class NodeBuilder {
 		/**
 		 * A reference to the current fog node.
 		 *
-		 * @type {?FogNode}
+		 * @type {?Node}
 		 * @default null
 		 */
 		this.fogNode = null;