[stdlib] Fix up types and nullability in the Core Image overlay.

rdar://problem/25372647

Author: jrose-apple

stdlib/public/SDK/CoreImage/CoreImage.swift

@@ -36,7 +36,7 @@ extension CIFilter {
   @available(iOS, introduced: 8.0)
   @available(OSX, introduced: 10.10)
   convenience init?(
-    name: String!, elements: (String, AnyObject)...
+    name: String, elements: (String, AnyObject)...
   ) {
     var dict: [String : AnyObject] = [:]
     for (key, value) in elements {
@@ -49,16 +49,16 @@ extension CIFilter {
 #if os(OSX)
 extension CISampler {
   // - (id)initWithImage:(CIImage *)im keysAndValues:key0, ...;
-  convenience init(im: CIImage!, elements: (NSCopying, AnyObject)...) {
-    let dict = NSMutableDictionary()
+  convenience init(im: CIImage, elements: (String, AnyObject)...) {
+    var dict: [String : AnyObject] = [:]
     for (key, value) in elements {
       dict[key] = value
     }
 
     // @objc(initWithImage:options:)
-    //   init(image im: CIImage!,
-    //        options dict: NSDictionary!)
-    self.init(image: im, options: dict as [NSObject: AnyObject])
+    //   init(image im: CIImage,
+    //        options dict: NSDictionary?)
+    self.init(image: im, options: dict)
   }
 }
 #endif