buildFunctionNode( shaderNode ) {

		const fn = new FunctionNode();

		const previous = this.currentFunctionNode;

		this.currentFunctionNode = fn;

		fn.code = this.buildFunctionCode( shaderNode );

		this.currentFunctionNode = previous;

		return fn;

	}
Returns the native shader operator name for a given generic name.
It is a similar type of method like {@link NodeBuilder#getMethod}.

@param {ShaderNodeInternal} shaderNode - The shader node to build the function node with.
@return {FunctionNode} The build function node.