[stdlib] Cover type difference in key path hash.

Include type metadata pointer in hashing.

(cherry picked from commit 731b9b0)

Author: dmcyk

stdlib/public/core/KeyPath.swift

@@ -59,6 +59,7 @@ public class AnyKeyPath: Hashable, _AppendKeyPath {
   ///   of this instance.
   @inlinable // FIXME(sil-serialize-all)
   final public func hash(into hasher: inout Hasher) {
+    hasher.combine(unsafeBitCast(type(of: self) as Any.Type, to: Int.self))
     return withBuffer {
       var buffer = $0
       while true {

test/stdlib/KeyPathImplementation.swift

@@ -680,6 +680,24 @@ keyPathImpl.test("equality") {
   expectNotEqual(s_c_z_p_x, s_c_z_p)
   expectNotEqual(s_c_z_p, s_c_z_p_x)
 
+  let s_x = WritableKeyPath<S<String>, Int>
+    .build(capacityInBytes: MemoryLayout<Int>.size + 4) {
+      $0.addHeader(trivial: true, hasReferencePrefix: false)
+      $0.addStructComponent(offset: S<String>.x_offset)
+    }
+
+  let si_x = WritableKeyPath<S<Int>, Int>
+    .build(capacityInBytes: MemoryLayout<Int>.size + 4) {
+      $0.addHeader(trivial: true, hasReferencePrefix: false)
+      $0.addStructComponent(offset: S<Int>.x_offset)
+    }
+
+  expectNotEqual(s_x, si_x)
+  expectNotEqual(s_x.hashValue, si_x.hashValue)
+
+  expectNotEqual(si_x, s_x)
+  expectNotEqual(si_x.hashValue, s_x.hashValue)
+
   // Same path, no reference prefix
   let s_c_z_p_x_readonly = KeyPath<S<S<String>>, Double>
     .build(capacityInBytes: 7 * MemoryLayout<Int>.size + 4) {