Add API to set use-markup on the child label
@debarshir
Submitted by Debarshi Ray Link to original bug (#743856)
Description
The GdHeaderButton interface in libgd had API to set the use-markup property on the child GtkLabel. It would be nice to be able to do the same with GtkButton.
Here is a use case: https://git.gnome.org/browse/gnome-documents/commit/?id=f7cc8e6027c2d41eaff29b8244f0cc813a424c5e
Version: 3.15.x