[SE-0258] Add @propertyDelegate and @propertyWrapper aliases

Fixes rdar://problem/51591955.

Author: DougGregor

include/swift/AST/Attr.def

@@ -404,6 +404,8 @@ DECL_ATTR(_custom, Custom,
 SIMPLE_DECL_ATTR(_propertyWrapper, PropertyWrapper,
   OnStruct | OnClass | OnEnum,
   86)
+DECL_ATTR_ALIAS(propertyDelegate, PropertyWrapper)
+DECL_ATTR_ALIAS(propertyWrapper, PropertyWrapper)
 SIMPLE_DECL_ATTR(_disfavoredOverload, DisfavoredOverload,
   OnAbstractFunction | OnVar | OnSubscript | UserInaccessible,
   87)

test/decl/var/property_wrapper_aliases.swift

@@ -0,0 +1,13 @@
+// RUN: %target-typecheck-verify-swift
+
+// expect-no-diagnostics
+
+@propertyDelegate
+struct Delegate<T> {
+  var value: T
+}
+
+@propertyWrapper
+struct Wrapper<T> {
+  var value: T
+}