Fix CIRawFilter intro issues

from Sebastien: "most filters are key-based natively (not-NSObject subclasses)) and we expose them as C# _user-type_ CIFilter-subclasses in recent years _most_ filters have also been exposed natively as protocols (not classes), we expose them as `*Protocol` interface types `CIRAWFilter` is a special case, it's a native `CIFilter` subclass so we're not using [CoreImageFilter] and [CoreImageFilterProperty] attributes to define it which also means we cannot use the "extra" tests to validate the filter properties. So we skip it here. Do not fear it's still tested, like any _normal_, NSObject subclass we have bound :-)"

tests/introspection/ApiCoreImageFiltersTest.cs

@@ -59,6 +59,8 @@ namespace Introspection {
 		protected virtual bool Skip (string nativeName)
 		{
 			switch (nativeName) {
+			case "CIRawFilter":
+				return true;
 			// Both reported in radar #21548819
 			//  NSUnknownKeyException [<CIDepthOfField 0x158586970> valueForUndefinedKey:]: this class is not key value coding-compliant for the key inputPoint2.
 			case "CIDepthOfField":