Not from NI, that I know of.
I did make a similar API that wraps the Qt framework. That involves creating external windows though; your toolkit has the benefit of being integrated with VI front panels.
Original LAVA post: https://lavag.org/topic/19611-utf-8-text-svg-images-inheritable-gui-components-dynamically-composed-guis-layout-management-splitters-in-tabs-mdis-taskbar-integration-and-much-more/
NIPM installation instructions: https://jksh.github.io/LQ-Bindings/docs/
As Mikael and Rolf said, class constants are not needed:
Definitely! LabVIEW's built-in support for dynamic GUIs is very poor. NXG was starting to show some promise with dynamic controls, but that's now dead. So, community-built tools are sorely needed.
Are you planning to make public releases of your work?
Layouts are common concept in a wide variety of GUI toolkits. Makes it so much easier to create resizable GUIs and support a variety of screen resolutions.