Feature request: expose more parts of the shadow DOM

[cgrisar]

FEATURE REQUEST

It is a bit frustrating that we can customize some parts of the shadow DOM but not every part of it.

For instance, when I style the context menu, I can't style a submenu differently than the main menu since both share
part(ui-menu-container) and part(menu-item).

Is there a way to add a specific part for the submenus? (ui-submenu-container, submenu-item)
And as an added bonus, when we customize the menuItems, to also allow to define a part in the menu-item?

like this

mf.MenuItems = [
{
label: "Cancel",
part: "cancel-menu-item",
onMenuSelect: () => mathField.insert ("\\cancel{#@}"),
}
...mf.menuItems,
]