Macro container_layer_accessors 

macro_rules! container_layer_accessors {
    () => { ... };
    (offset) => { ... };
}

Implements the ContainerLayer field accessors for a container_layer field.

container_layer_accessors!(offset) also records that the type extends OffsetLayer, so its AnyContainerLayer can be narrowed with AnyContainerLayer::as_offset_layer.