XDG Portals provide a plethora of features meant to be used inside and
outside sandboxed environments. OBS Studio currently uses portals to
implement Wayland-compatible monitor and window captures.
However, OBS Studio performs another action that can be done through
portals: inhibit the screensaver. Under the Desktop portal (the same
used by the captures mentioned above), there is an "Inhibit" portal
that provides session inhibition.
Add a new portal-based inhibitor. This inhibitor is only used when the
Desktop portal is available and running; the previous D-Bus implementation
is used in the absence of the portal. Because it's basically another set
of D-Bus operations, wrap the new portal inhibitor under the HAVE_DBUS
call too.
