[Native] Implement the macOS/Cocoa and Gtk File Dialogs

[zbaylin]

EDIT: This is now fixed, and there is more information below.

This provides bindings to NSOpenPanel. This is in response to #444 by @Et7f3.

I'm so close, but for some reason, I keep getting strange memory errors on any operations on the string(s) returned.

For example, the code

Console.log("WORKS:");
Console.log(x);
Console.log("CRASHES:");
Console.log("" ++ x);

results in

Hopefully some fresh eyes can help with this.

@Et7f3, any help would be greatly appreciated!

[Et7f3]

Can you select file extention ? like "*.txt". On windows we can. It may be useful to add function to generate the string if it haven't the same syntax.

[zbaylin]

yes you can -- I haven't pushed it yet but I will when I get back home.

[zbaylin]

I fixed the alloc error. It was a result of me mistakenly adding [@noalloc] before my external declaration. Now the dialog is fully functional. I will add more functionality to it (changing the "OK" button text, allowing opening directories, disallowing opening files, etc.)

[zbaylin]

I also am now adding bindings to the Gtk/Linux file dialog.

[bryphe]

Thank you @zbaylin and @Et7f3 ! This is awesome!