11:11 Hiroki Tagato (tagattie) 

deskutils/libportal: split into slave ports corresponding to GUI backend

The port has been splitted into 1 master and 3 slave ports for those
who want only a subset of the supported backends and don't want
excessive dependency, namely:
- deskutils/libportal:      common non-GUI part (master port)
- deskutils/libportal-gtk3: gtk3 backend
- deskutils/libportal-gtk4: gtk4 backend
- deskutils/libportal-qt5:  qt5 backend

While here, correct license and make dependency adjustments of
consumer ports.

PR:		269546
Reviewed by:	arrowd
Approved by:	arrowd (maintainer)

    03396f7