New use flag builds Qt5 plugin for integration with flatpak and snap.
Add missing IUSE=gtk dependencies. No additional dependencies with
IUSE=dbus means the added REQUIRED_USE is cheap, and sys-apps/dbus is
already pulled in by x11-libs/gtk+3 (via dev-libs/glib) unconditionally.
Switch from ~PV to =QT5_PV* version dependencies.
Package-Manager: Portage-3.0.23, Repoman-3.0.3
Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>