Cleanup: move public doc-strings into headers for 'modifiers'

Ref T92709

source/blender/modifiers/MOD_nodes.h

@@ -24,6 +24,11 @@ struct Object;
 extern "C" {
 #endif
 
+/**
+ * Rebuild the list of properties based on the sockets exposed as the modifier's node group
+ * inputs. If any properties correspond to the old properties by name and type, carry over
+ * the values.
+ */
 void MOD_nodes_update_interface(struct Object *object, struct NodesModifierData *nmd);
 
 void MOD_nodes_init(struct Main *bmain, struct NodesModifierData *nmd);