nodeBuilder: Add abstract reference for buildFunctionCode (#30712)

Co-authored-by: Samuel Rigaud <srigaud@duodisplay.com>

src/nodes/core/NodeBuilder.js

@@ -2176,6 +2176,19 @@ class NodeBuilder {
 
 	}
 
+	/**
+	 * Builds the given shader node.
+	 *
+	 * @abstract
+	 * @param {ShaderNodeInternal} shaderNode - The shader node.
+	 * @return {string} The function code.
+	 */
+	buildFunctionCode( /* shaderNode */ ) {
+
+		console.warn( 'Abstract function.' );
+
+	}
+
 	/**
 	 * Generates a code flow based on a child Node.
 	 *