monitor-manager: Take drm-connector panel-orientation property into account

Some x86 clamshell design devices use portrait tablet LCD panels while
they should use a landscape panel, resoluting in a 90 degree rotated
picture.

Newer kernels detect this and rotate the fb console in software to
compensate. These kernels also export their knowledge of the LCD panel
orientation vs the casing in a "panel orientation" drm_connector property.

This commit adds support to mutter for reading the "panel orientation"
and transparently (from a mutter consumer's pov) fixing this by applying
a (hidden) rotation transform to compensate for the panel orientation.

Related: https://bugs.freedesktop.org/show_bug.cgi?id=94894

https://bugzilla.gnome.org/show_bug.cgi?id=782294

src/backends/meta-monitor.h

@@ -145,6 +145,16 @@ const char * meta_monitor_get_serial (MetaMonitor *monitor);
 
 MetaConnectorType meta_monitor_get_connector_type (MetaMonitor *monitor);
 
+/* This function returns the transform corrected for the panel orientation */
+MetaMonitorTransform meta_monitor_logical_to_crtc_transform (MetaMonitor          *monitor,
+                                                             MetaMonitorTransform  transform);
+/*
+ * This function converts a transform corrected for the panel orientation
+ * to its logical (user-visible) transform.
+ */
+MetaMonitorTransform meta_monitor_crtc_to_logical_transform (MetaMonitor          *monitor,
+                                                             MetaMonitorTransform  transform);
+
 uint32_t meta_monitor_tiled_get_tile_group_id (MetaMonitorTiled *monitor_tiled);
 
 gboolean meta_monitor_get_suggested_position (MetaMonitor *monitor,