[macos] Multiple Accessibility APIs missing

This code works in ObjC:

```objc
NSPopUpButton *p = [[NSPopUpButton alloc] init];
p.accessibilityIdentifier = @"hello";
NSString *result = p.accessibilityIdentifier;
```

But this does not in C#:

```csharp
NSPopUpButton button = new NSPopUpButton ();
button.AccessibilityIdentifier = "hello";
var result = button.AccessibilityIdentifier;
```

It comes off the full set in:

```objc
@protocol NSAccessibility
@required
```