backends/native: Change handling of display mapping for rel tablet tools

We avoided setting the device matrix applying to the tablet tool (used if the
tablet is in absolute coordinates mode) if the device is configured for relative
motion, but forgot to apply the matrix if changing the device back to absolute
mode, this made the device seemingly forget its attached display until later
configuration changes.

In order to avoid the hassle of looking up the right display again on unrelated
configuration changes, make the matrix be always set on the device, but only
actually used in absolute coordinates mode. This makes the device able to
seamlessly switch between modes and remain mapped to the right display.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3012>

src/backends/native/meta-input-device-native.c

@@ -1592,6 +1592,9 @@ meta_input_device_native_translate_coordinates_in_impl (ClutterInputDevice *devi
   float stage_width, stage_height;
   double x_d, y_d;
 
+  if (device_evdev->mapping_mode == META_INPUT_DEVICE_MAPPING_RELATIVE)
+    return;
+
   meta_viewport_info_get_extents (viewports, &stage_width, &stage_height);
   x_d = *x / stage_width;
   y_d = *y / stage_height;

src/backends/native/meta-input-settings-native.c

@@ -138,20 +138,9 @@ set_matrix (GTask *task)
   float *matrix = g_task_get_task_data (task);
   cairo_matrix_t dev_matrix;
 
-  if (clutter_input_device_get_device_type (device) ==
-      CLUTTER_TOUCHSCREEN_DEVICE ||
-      meta_input_device_native_get_mapping_mode_in_impl (device) ==
-      META_INPUT_DEVICE_MAPPING_ABSOLUTE)
-    {
   cairo_matrix_init (&dev_matrix,
                      matrix[0], matrix[3], matrix[1],
                      matrix[4], matrix[2], matrix[5]);
-    }
-  else
-    {
-      cairo_matrix_init_identity (&dev_matrix);
-    }
-
   g_object_set (device, "device-matrix", &dev_matrix, NULL);
 
   return G_SOURCE_REMOVE;