Assets: Implement viewport drag and drop for geometry nodes

Currently there's no way to assign a geometry node group from the asset
browser to an object as a modifier without first appending/linking it
manually. This patch adds a drag and drop operator that adds a new
modifier and assigns the dragged tree.

@@ -2870,0 +2873,4 @@
+/** \name Drop Geometry Nodes on Object Operator
+ * \{ */
+
+char *ED_object_ot_drop_geometry_nodes_tooltip(bContext *C,

@@ -2870,0 +2888,4 @@
+    return BLI_strdup("");
+  }
+
+  const char *tooltip = TIP_("Drop node tree %s on object %s");

@@ -705,0 +729,4 @@
+    }
+    if (wmDropBox *drop_box = drag->drop_state.active_dropbox) {
+      const uint32_t uuid = RNA_int_get(drop_box->ptr, "session_uuid");
+      bNodeTree *node_tree = reinterpret_cast<bNodeTree *>(