add `ComboListCell`

[typemytype]

import AppKit

def ComboListCell(items, completes=True):    
    """
     An object that displays a combo box in a List column.

    **This object should only be used in the *columnDescriptions*
    argument during the construction of a List.**

    **items** The items that should appear in the combo box.
    
    **completes** Boolean representing if the combo box auto completes entered text.
    
    Example:
        
        from vanilla import *

        class ComboListCellDemo(object):

            def __init__(self):
                self.w = Window((200, 300), minSize=(100, 100))
                self.w.myList = List((0, 0, -0, -0),
                            [{"value": "a"}],
                            columnDescriptions=[
                                {
                                    "title": "value",
                                    "cell": ComboListCell(["a", "b", "c", "hello", "world"]),
                                },
                            ],
                            editCallback=self.editCallback)
                self.w.open()

            def editCallback(self, sender):
                print(sender.get())

        ComboListCellDemo()
    """
    cell = AppKit.NSComboBoxCell.alloc().init()
    cell.setButtonBordered_(False)
    cell.setBordered_(False)
    cell.setDrawsBackground_(False)
    cell.setEditable_(True)
    cell.setCompletes_(completes)
    cell.setControlSize_(AppKit.NSMiniControlSize)
    titles = []
    for title in items:
        if isinstance(title, (AppKit.NSString, AppKit.NSAttributedString)):
            title = title.string()
        titles.append(title)
    cell.addItemsWithObjectValues_(titles)
    return cell



from vanilla import *

class ComboListCellDemo(object):

    def __init__(self):
        self.w = Window((200, 300), minSize=(100, 100))
        self.w.myList = List((0, 0, -0, -0),
                    [{"value": "a"}],
                    columnDescriptions=[
                        {
                            "title": "value",
                            "cell": ComboListCell(["a", "b", "c", "hello", "world"]),
                        },
                    ],
                    editCallback=self.editCallback)
        self.w.open()

    def editCallback(self, sender):
        print(sender.get())

ComboListCellDemo()