[KeyPath] Fix regression in == on keypaths

Author: kubamracek

stdlib/public/core/KeyPath.swift

@@ -237,12 +237,10 @@ extension AnyKeyPath: Hashable {
     if a === b {
       return true
     }
-    /*
     // Short-circuit differently-typed key paths
     if type(of: a) != type(of: b) {
       return false
     }
-    */
     return a.withBuffer {
       var aBuffer = $0
       return b.withBuffer {

test/stdlib/KeyPath.swift

@@ -327,6 +327,14 @@ keyPath.test("computed properties") {
   }
 }
 
+keyPath.test("equality") {
+  expectNotEqual(\Array<String>.isEmpty, \Substring.isEmpty)
+  expectNotEqual(\Array<String>.isEmpty, \Substring.isEmpty)
+  expectNotEqual(\Array<String>.isEmpty, \String.isEmpty)
+  expectNotEqual(\Array<String>.isEmpty, \Substring.last)
+  expectNotEqual(\Array<String>.isEmpty, \Array<Substring>.isEmpty)
+}
+
 class AB {
 }
 class ABC: AB, ABCProtocol {