postprocessing: Use QgsLayerTreeRegistryBridge to add layers

When a profile tool is already opened, the output of a procssing is
not added to its layer tree. This is because it relies on a
`QgsLayerTreeRegistryBridge`. Indeed, `QgsLayerTreeRegistryBridge`
listens to the `QgsProject::legendLayersAdded()` signal in order to
update the elevation profile tree view. However this signal is not
triggered by the current logic in `Postprocessing.py`because
`QgsProject::addMaplayer` is called with `addToLegend` set to
False. Then, the layer is added to the tree by calling
`QgsLayerTreeGroup::insertChildNode`.

This issue is fixed by creating a
`QgsLayerTreeRegistryBridge::InsertionPoint` to set the insertion
point and then calling `QgsProject::addMaplayer` with `addToLegend`
set to True.

python/plugins/processing/gui/Postprocessing.py

@@ -35,6 +35,7 @@
     QgsLayerTreeLayer,
     QgsLayerTreeGroup,
     QgsLayerTreeNode,
+    QgsLayerTreeRegistryBridge,
 )
 from qgis.utils import iface
 
@@ -237,8 +238,6 @@ def handleAlgorithmResults(
                 # output layer already exists in the destination project
                 owned_map_layer = context.temporaryLayerStore().takeMapLayer(layer)
                 if owned_map_layer:
-                    details.project.addMapLayer(owned_map_layer, False)
-
                     # we don't add the layer to the tree yet -- that's done
                     # later, after we've sorted all added layers
                     layer_tree_layer = create_layer_tree_layer(owned_map_layer, details)
@@ -289,11 +288,20 @@ def handleAlgorithmResults(
                 current_node_index = current_node_group.children().index(
                     current_selected_node
                 )
-                current_node_group.insertChildNode(current_node_index, layer_node)
+                insertion_point = QgsLayerTreeRegistryBridge.InsertionPoint(
+                    current_node_group, current_node_index
+                )
             elif isinstance(current_selected_node, QgsLayerTreeGroup):
-                current_selected_node.insertChildNode(0, layer_node)
+                insertion_point = QgsLayerTreeRegistryBridge.InsertionPoint(
+                    current_selected_node, 0
+                )
             elif context.project():
-                context.project().layerTreeRoot().insertChildNode(0, layer_node)
+                insertion_point = QgsLayerTreeRegistryBridge.InsertionPoint()
+
+            details.project.layerTreeRegistryBridge().setLayerInsertionPoint(
+                insertion_point
+            )
+            details.project.addMapLayer(owned_map_layer)
 
         if not have_set_active_layer and iface is not None:
             iface.setActiveLayer(layer_node.layer())