table: no way to prevent row context menu when right-clicking header

[boboshan]

Problem

When using TableDelegate::render_th() with ContextMenuExt to add context menus to column headers, right-clicking a header shows both the row context menu and the header context menu simultaneously.

Root cause

The row context menu is attached to inner_table (in render() at state.rs ~line 1973), which wraps both the header and body. When right-clicking a header cell:

1. The inner_table context menu fires because the header is geometrically inside its bounds
2. It reads right_clicked_row which may still be Some from a previous row click
3. The header's own context menu (from ContextMenuExt) also opens independently
4. Both menus appear at the same time

The on_mouse_down_out dismiss handler on the row menu doesn't fire because the click is inside inner_table's bounds.

Workaround

I overrode render_header to add on_mouse_down(MouseButton::Right) that clears the row state before menu builders run. However, right_clicked_row is private, so I forked and added:

pub fn clear_right_clicked_row(&mut self) {
    self.right_clicked_row = None;
}

Suggested fix

Either:

1. Expose clear_right_clicked_row() (or a set_right_clicked_row) as a public method on TableState
2. Add a header_context_menu() method to TableDelegate (similar to context_menu() for rows) that the framework handles correctly
3. Window-level context menu tracking so opening any context menu auto-dismisses others

Option 1 is the smallest change. Option 2 is the cleanest API.

Reproduction

impl TableDelegate for MyDelegate {
    fn render_th(&mut self, col_ix: usize, _window: &mut Window, cx: &mut Context<TableState<Self>>) -> impl IntoElement {
        div()
            .id(("th", col_ix))
            .child("Header")
            .context_menu(|menu, _w, _cx| {
                menu.item(PopupMenuItem::new("Header action"))
            })
    }

    fn context_menu(&mut self, row_ix: usize, menu: PopupMenu, ...) -> PopupMenu {
        menu.item(PopupMenuItem::new("Row action"))
    }
}

Steps: Right-click a row → right-click a column header → two menus appear.