Add a new setExclusiveEdge call in the protocol

This can be used to disambiguate the exclusive edge when the anchors are
on a corner (so there  would be 2 candidates)

it's quite quick and dirty mostly to understand if we do want to push
for something along the lines


(cherry picked from commit ad5246f0d0)

src/qwaylandlayershellintegration.cpp

@@ -15,7 +15,7 @@
 namespace LayerShellQt
 {
 QWaylandLayerShellIntegration::QWaylandLayerShellIntegration()
-    : QWaylandShellIntegrationTemplate<QWaylandLayerShellIntegration>(4)
+    : QWaylandShellIntegrationTemplate<QWaylandLayerShellIntegration>(5)
     , m_xdgActivation(new QWaylandXdgActivationV1)
 {
 }