Merge pull request swiftlang#20791 from slavapestov/small-abi-nit

stdlib: __SwiftNativeNSString does not need to be public

Author: slavapestov

stdlib/public/core/StringBridge.swift

@@ -267,12 +267,9 @@ extension String {
 // The @_swift_native_objc_runtime_base attribute
 // This allows us to subclass an Objective-C class and use the fast Swift
 // memory allocator.
-@_fixed_layout // FIXME(sil-serialize-all)
 @objc @_swift_native_objc_runtime_base(__SwiftNativeNSStringBase)
-public class __SwiftNativeNSString {
-  @usableFromInline // FIXME(sil-serialize-all)
-  @objc
-  internal init() {}
+class __SwiftNativeNSString {
+  @objc internal init() {}
   deinit {}
 }
 

test/api-digester/Outputs/stability-stdlib-abi.swift.expected

@@ -498,3 +498,5 @@ Func LazyCollectionProtocol.map(_:) has been removed
 Func LazyCollectionProtocol.prefix(while:) has been removed
 Func LazyCollectionProtocol.reversed() has been removed
 Var LazyCollectionProtocol.lazy has declared type change from LazyCollection<τ_0_0.Elements> to LazySequence<τ_0_0.Elements>
+
+Class __SwiftNativeNSString has been removed