Migrate from UnsafePointer<Void> to UnsafeRawPointer. (#3724)

* Migrate from `UnsafePointer<Void>` to `UnsafeRawPointer`.

As proposed in SE-0107: UnsafeRawPointer.

`void*` imports as `UnsafeMutableRawPointer`.
`const void*` imports as `UnsafeRawPointer`.

Occurrences of `UnsafePointer<Void>` are replaced with UnsafeRawPointer.

* Migrate overlays from UnsafePointer<Void> to UnsafeRawPointer.

This requires explicit memory binding in several places,
particularly in NSData and CoreAudio.

* Fix a bunch of test cases for Void->Raw migration.

* qsort takes IUO values

* Bridge `Unsafe[Mutable]RawPointer as `void [const] *`.

* Parse #dsohandle as UnsafeMutableRawPointer

* Update a bunch of test cases for Void->Raw migration.

* Trivial fix for the SceneKit test case.

* Add an UnsafeRawPointer self initializer.

This is unfortunately necessary for assignment between types imported from C.

* Tiny simplification of the initializer.

stdlib/public/SDK/Foundation/NSError.swift

@@ -41,7 +41,7 @@ internal func NS_Swift_performErrorRecoverySelector(
   delegate: AnyObject?,
   selector: Selector,
   success: ObjCBool,
-  contextInfo: UnsafeMutablePointer<Void>?)
+  contextInfo: UnsafeMutableRawPointer?)
 
 /// Class that implements the informal protocol
 /// NSErrorRecoveryAttempting, which is used by NSError when it
@@ -52,7 +52,7 @@ class _NSErrorRecoveryAttempter {
                        optionIndex recoveryOptionIndex: Int,
                        delegate: AnyObject?,
                        didRecoverSelector: Selector,
-                       contextInfo: UnsafeMutablePointer<Void>?) {
+                       contextInfo: UnsafeMutableRawPointer?) {
     let error = nsError as Error as! RecoverableError
     error.attemptRecovery(optionIndex: recoveryOptionIndex) { success in
       NS_Swift_performErrorRecoverySelector(