grid: Use the proper orientation for the request mode
grid: Use the proper orientation for the request mode

We automatically switch the request mode of the container depending on
the GridLayout's orientation, but we need to keep track of the request
mode during allocation, so that we don't get out of sync if the user
changed the request mode after adding the layout manager.

This change also brings us closer to the code in GtkGrid.

jigpu/clutter,jigpu/clutter,Distrotech/clutter,Distrotech/clutter,GNOME/clutter,Distrotech/clutter,GNOME/clutter,Distrotech/clutter,GNOME/clutter,jigpu/clutter,Distrotech/clutter,jigpu/clutter,jigpu/clutter,jigpu/clutter,GNOME/clutter,GNOME/clutter,Distrotech/clutter