[NEW] x11-toolkits/guile-gnome-platform: Guile bindings for Gnome

This the final addition to complete the set of ports enabling the use of
Gnome GUI from Guile scripts.

WWW: https://www.gnu.org/software/guile-gnome/

PR: 241731
Submitted by: Andrew <andrew tao11 riddles org uk>
Reviewed by: mat (flavors)
Differential Revision: https://reviews.freebsd.org/D22189