[Foundation] Switch to private imports of Foundation shims

Author: lorentey

stdlib/public/Darwin/Foundation/Calendar.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 /**
  `Calendar` encapsulates information about systems of reckoning time in which the beginning, length, and divisions of a year are defined. It provides information about the calendar and support for calendrical computations such as determining the range of a given calendrical unit and adding units to a given absolute time.

stdlib/public/Darwin/Foundation/CharacterSet.swift

@@ -13,7 +13,7 @@
 @_exported import Foundation // Clang module
 import CoreFoundation
 import _SwiftCoreFoundationOverlayShims
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 private func _utfRangeToCFRange(_ inRange : Range<Unicode.Scalar>) -> CFRange {
     return CFRange(

stdlib/public/Darwin/Foundation/Data.swift

@@ -41,7 +41,7 @@ internal func __NSDataIsCompact(_ data: NSData) -> Bool {
 #else
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 import _SwiftCoreFoundationOverlayShims
 
 internal func __NSDataIsCompact(_ data: NSData) -> Bool {

stdlib/public/Darwin/Foundation/FileManager.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 extension FileManager {
     /*

stdlib/public/Darwin/Foundation/IndexPath.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 /**
  `IndexPath` represents the path to a specific node in a tree of nested array collections.

stdlib/public/Darwin/Foundation/IndexSet.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 extension IndexSet.Index {
     public static func ==(lhs: IndexSet.Index, rhs: IndexSet.Index) -> Bool {

stdlib/public/Darwin/Foundation/Locale.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 /**
  `Locale` encapsulates information about linguistic, cultural, and technological conventions and standards. Examples of information encapsulated by a locale include the symbol used for the decimal separator in numbers and the way dates are formatted.

stdlib/public/Darwin/Foundation/NSCoder.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 //===----------------------------------------------------------------------===//
 // NSCoder

stdlib/public/Darwin/Foundation/NSDictionary.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 @_exported import Foundation // Clang module
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 // We don't check for NSCopying here for performance reasons. We would
 // just crash anyway, and NSMutableDictionary will still do that when

stdlib/public/Darwin/Foundation/NSError.swift

@@ -13,7 +13,7 @@
 @_exported import Foundation // Clang module
 import CoreFoundation
 import Darwin
-import _SwiftFoundationOverlayShims
+@_implementationOnly import _SwiftFoundationOverlayShims
 
 //===----------------------------------------------------------------------===//
 // NSError (as an out parameter).