Add nsmenu title

[terhechte]

This is an initial fix for #1835.

It uses ::alloc().initWithTitle(...) to initialize NSMenu items with a correct title.
However, it is not clear to me yet what the behaviour would be for the Menu that is exposed from the druid crate.
Right now I'm calling Menu("") but I suppose that's wrong. My guess would be that the public druid API would also expose a title property? But then it would affect all platforms. Open to suggestions here :)

[cmyr]

I think that initing with an empty string and then modifying it afterwards to the correct title should be okay?

[terhechte]

Updated it accordingly to use an empty string and added set_title which only works on macOS and is a NOP on the other platforms

[kud1ing]

maybe just "File"?

[cmyr]

Okay so I'm looking at this again, and I want to double-check my understanding:

• druid-shell's Menu::new method is only called for root menus; that means the root application menu, as well as root popup menus.
• all other items (such as the file menu) are created with the add_item and add_dropdown, which do correctly set titles

And in both the case of. the root menu and of a context menu, the title is (I believe) unused?

Ultimately I'm wondering if we need to bother with the whole set_title addition. My main concern with #1835 isn't with the title not being set, it's with a missing init call that may be performing other important work. If we can just init with an empty string and leave it at that, I'd be happy for the simplification..

[terhechte]

@cmyr I agree. I've removed the set_title implementations. Just using an empty string should be enough.

[cmyr]

Thanks!