Allow frontends/GUIs and C plugins to use select.lua

Expected behavior of the wanted feature

With uosc.lua and commnd_palette.lua this is possible. Both use the same API, commnd_palette.lua implements it only partly.

From https://github.com/natural-harmonia-gropius/recent-menu/blob/master/recentmenu.lua#L279

function open_menu_uosc()
    local json = utils.format_json(menu)
    mp.commandv("script-message-to", "uosc", "open-menu", json)
end

function open_menu_command_palette()
    local json = utils.format_json(menu)
    mp.commandv("script-message-to",
        "command_palette",
        "show-command-palette-json", json)
end

From commnd_palette.lua:

mp.register_script_message("show-command-palette-json", function (json)
    if dpiScale == 0 then
        dpiScale = mp.get_property_native("display-hidpi-scale", 1)
    end

    o.font_size = originalFontSize * dpiScale

    local menu_data = utils.parse_json(json)
    menu_content.list = {}
    menu_content.current_i = 1
    menu.search_heading = menu_data.title
    menu.filter_by_fields = { "content", "hint", "value_hint" }
    em.get_line = original_get_line_func

    for k, v in ipairs(menu_data.items) do
        local values = v.value

        if type(values) == "string" then
            values = { values }
        end

        table.insert(menu_content.list, {
            index = k,
            content = v.title,
            hint = v.hint,
            values = values,
            value_hint = table.concat(values, " "),
        })

        if menu_data.selected_index then
            menu_content.current_i = menu_data.selected_index
        end
    end

    function menu:submit(tbl)
        mp.command_native(tbl.values)
    end

    hide_osc()
    menu:init(menu_content)
end)

From mpv.net

    void ShowRecentFilesInCommandPalette()
    {
        Obj o = new();
        o.title = "Recent Files";
        o.selected_index = 0;

        var items = new List<Item>();

        foreach (string file in App.Settings.RecentFiles)
        {
            items.Add(new Item() { title = Path.GetFileName(file),
                value = ["loadfile", file],
                hint = file});
        }

        o.items = [.. items];
        string json = JsonSerializer.Serialize(o);
        Player.CommandV("script-message", "show-command-palette-json", json);
    }

@natural-harmonia-gropius

Start by reading select.lua and comparing the uosc.lua, commnd_palette.lua, recentmenu.lua, and mpv.net examples cited in the issue. Determine the API needed for frontends/GUIs and C plugins to use select.lua, then verify that the demonstrated menu data and command submission flows work through that API.