Panel Layout Designer

Add a tab to the Text Editor called Panel Layout Designer similar to the Icon Viewer addon.

It would display a blank panel and a toolbar of available graphical elements that can be placed like rows, columns, grid_flow, operator buttons with an icon/text, text fields, labels and align, scale_x options....etc

In addition to the icons already available in Blender, custom icons could be imported as base64 strings.

Clicking on an element placed in the panel would display the available attributes for that object in a side panel.

The Panel Layout Designer would have a View->Design mode and View->Layout code. The layout code could be copied and pasted into your own python addon script.