[stdlib] Clean up some sources of undefined behaviour

While experimenting with forbidding temporary argument conversions for `UnsafePointer` initialiser parameters (amongst others), I found a few cases where we're currently making such unsound calls in the SDK overlays.

This commit removes such usages by performing the temporary argument conversions directly without going through any `UnsafePointer` initialiser calls first.

In the case of `MTLCopyAllDevicesWithObserver`, we were even over-releasing the observer through the usage of:

```swift
AutoreleasingUnsafeMutablePointer<NSObjectProtocol?>(&resultTuple.observer)
```

As we're treating +1 memory as having +0 semantics (this didn't appear to cause issues for users though as Metal itself appears to keep the observer retained).

Author: hamishknight

stdlib/public/SDK/CoreGraphics/CoreGraphics.swift

@@ -517,7 +517,7 @@ extension CGAffineTransform : Codable {
 
 extension CGImage {
   public func copy(maskingColorComponents components: [CGFloat]) -> CGImage? {
-    return self.__copy(maskingColorComponents: UnsafePointer(components))
+    return self.__copy(maskingColorComponents: components)
   }
 }
 

stdlib/public/SDK/Metal/Metal.swift

@@ -100,10 +100,11 @@ extension MTLDevice {
 @available(swift 4)
 @available(macOS 10.13, *)
 public func MTLCopyAllDevicesWithObserver(handler: @escaping MTLDeviceNotificationHandler) -> (devices:[MTLDevice], observer:NSObject) {
-    var resultTuple: (devices:[MTLDevice], observer:NSObject)
-    resultTuple.observer = NSObject()
-    resultTuple.devices = __MTLCopyAllDevicesWithObserver(AutoreleasingUnsafeMutablePointer<NSObjectProtocol?>(&resultTuple.observer), handler)
-    return resultTuple
+    var observer: NSObjectProtocol?
+    let devices = __MTLCopyAllDevicesWithObserver(&observer, handler)
+    // FIX-ME: The force cast here isn't great – ideally we would return the
+    // observer as an NSObjectProtocol.
+    return (devices, observer as! NSObject)
 }
 #endif
 

stdlib/public/SDK/SceneKit/SceneKit.swift.gyb

@@ -179,15 +179,15 @@ extension SCNGeometryElement {
 extension SCNGeometrySource {
   @nonobjc
   public convenience init(vertices: [SCNVector3]) {
-    self.init(vertices: UnsafePointer(vertices), count: vertices.count)
+    self.init(vertices: vertices, count: vertices.count)
   }
   @nonobjc
   public convenience init(normals: [SCNVector3]) {
-    self.init(normals: UnsafePointer(normals), count: normals.count)
+    self.init(normals: normals, count: normals.count)
   }
   @nonobjc
   public convenience init(textureCoordinates: [CGPoint]) {
-    self.init(textureCoordinates: UnsafePointer(textureCoordinates), count: textureCoordinates.count)
+    self.init(textureCoordinates: textureCoordinates, count: textureCoordinates.count)
   }
 }