Make egu::menu types public

[sor-ca]

Sometimes we need to fix the current state of the application in the moment when you open the context menu, to save it, and to use it during creation of context menu and response handling. Making some structs, related with menu creating, allow us to create functions for this cases. For example,

pub fn context_menu_custom<'a, T>(
    response: &Response,
    //variable for fixing state in the moment when you open context menu
    state: &mut T,
    //function which allow to get some king of state.
    //In this case state depends on cursor position, in other cases it may depend on system time or something else
    get_state: impl FnOnce(Pos2) -> T,
    //set contents of menu depending on state
    set_contents: impl 'a + FnOnce(&T) -> Box<dyn 'a + FnOnce(&mut Ui)>,
) -> Option<InnerResponse<()>> {
    let menu_id = Id::new("__egui::context_menu");
    let mut bar_state = BarState::load(&response.ctx, menu_id);
    let root = &mut bar_state;

    let menu_response = MenuRoot::context_interaction(response, root);
    if let egui::menu::MenuResponse::Create(p, _) = &menu_response {
        *state = get_state(*p);
    };

    let add_contents = set_contents(&state);

    MenuRoot::handle_menu_response(root, menu_response);
    let inner_response = bar_state.show(response, add_contents);

    bar_state.store(&response.ctx, menu_id);
    inner_response
}

The example of using such function you may see in my repository
It is very simple example, and is this case, the problem may be solved without fn context_menu_custom, but in more complex situations, it may be very useful
Related issue: #4162

[sor-ca]

Шs there anything else I need to add or did you want me to add a description only to MenuState struct?

[emilk]

No - just get the CI green and I can hit merge

[sor-ca]

Thank you, I've done it