[stdlib] Properly generalize ObjectIdentifier.init(Any.Type)

With Slava’s fix in swiftlang#79647, we can now refer to generalized type existentials in ABI stable code.

Author: lorentey

stdlib/public/core/ObjectIdentifier.swift

@@ -61,23 +61,15 @@ public struct ObjectIdentifier: Sendable {
   ///
   /// - Parameters:
   ///   - x: A metatype.
-  @inlinable // trivial-implementation
-  public init(_ x: Any.Type) {
+  @_alwaysEmitIntoClient
+  public init(_ x: any (~Copyable & ~Escapable).Type) {
     self._value = unsafe unsafeBitCast(x, to: Builtin.RawPointer.self)
   }
 
-  /// Creates an instance that uniquely identifies the given metatype.
-  ///
-  /// - Parameters:
-  ///   - x: A metatype.
-  @_alwaysEmitIntoClient
-  @_disfavoredOverload
-  public init<T: ~Copyable & ~Escapable>(_ x: T.Type) {
-    // FIXME: This should rather use an existential:
-    // FIXME:    init(_ x: any (~Copyable & ~Escapable).Type)
-    // FIXME: Unfortunately, that syntax does not survive into the
-    // FIXME: swiftinterface. rdar://139465298
-    self._value = unsafeBitCast(x, to: Builtin.RawPointer.self)
+  @_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
+  @usableFromInline
+  internal init(_ x: Any.Type) {
+    self._value = unsafe unsafeBitCast(x, to: Builtin.RawPointer.self)
   }
 }