Regression: cannot add new nodes inline

[Keavon]

This is a regression introduced in #3337.

The button to add a new node inline to the selected layer (found in the Properties panel, Layers panel, and node graph control bar) no longer functions when a node is clicked. For example, draw a rectangle and search this menu for "Repeat" and try clicking to add it.

warn editor/src/messages/layout/layout_message_handler.rs:116
handle_widget_callback was called referencing an invalid widget ID, although the layout target was valid. widget_id: 154848269268510619, layout_target: PropertiesPanel

A related second regression that's likely caused by the same root issue:

The Overlays popover menu's checkbox options do not do anything anymore, and upon closing the menu and reopening it, they return to their originally checked states: