It would be nice if CTFont constructor's matrix parameter was "in" instead of "ref"

This might be a problem throughout Xamarin.Mac and Monotouch, but CTFont constructor is currently defined as:

```cs
public CTFont(CTFontDescriptor descriptor, nfloat size, CTFontOptions options, ref CGAffineTransform matrix);
```

whereas the native side is:

```cs
CTFontRef CTFontCreateWithName ( CFStringRef name, CGFloat size, const CGAffineTransform *matrix );
```

not being an "in" parameter means I can't pass a temporary object to the constructor, which is a very minor but avoidable PITA, if the native API was bound better.

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Source: https://bugzilla.xamarin.com/28/28349/bug.html