Revert "xdg-desktop-portal: Don't ship the x-cinnamon-portals.conf file."

This reverts commit 13ab48c.

Relying on the legacy portal ends up breaking the dark/light setting.
The reverted commit fixed the settings portal's 'ReadAll' method,
but apparently broke 'Read', which is what libadwaita (and most
others) use to get the 'color-scheme' setting.

Author: mtwebster

data/xdg-portal/meson.build

@@ -1,4 +1,4 @@
-# install_data(
-#   'x-cinnamon-portals.conf',
-#   install_dir: join_paths(get_option('datadir'), 'xdg-desktop-portal'),
-# )
+install_data(
+  'x-cinnamon-portals.conf',
+  install_dir: join_paths(get_option('datadir'), 'xdg-desktop-portal'),
+)

debian/cinnamon.install

@@ -4,3 +4,4 @@ usr/libexec
 usr/share/applications
 usr/share/dbus-1
 usr/share/man
+usr/share/xdg-desktop-portal