The simpliest workaround is to use B4A. Create a new project. Open a Designer and edit properties for Button1. Set TypeFace to FontAwesome and click line FontAwesome ... Find an icon and click it (to copy to clipboard). Switch to B4i designer. Paste (Ctrl-V) into Text property. Unlike you will see a square box in B4i Designer, in run-time everything looks correct.
The simpliest workaround is to use B4A. Create a new project. Open a Designer and edit properties for Button1. Set TypeFace to FontAwesome and click line FontAwesome ... Find an icon and click it (to copy to clipboard). Switch to B4i designer. Paste (Ctrl-V) into Text property. Unlike you will see a square box in B4i Designer, in run-time everything looks correct.
The exact way is to add in Designer two additional lines: FontAwesome .... and Material Icons ... , like for Labels. Buttons etc.
Probably, it will be done in future releases, but just now it's necessary to use a workaround (Erel's suggestion works also).