Make AdditiveArithmetic.zero @_transparent (swiftlang#25658)

Author: t-ae

stdlib/public/core/Integers.swift

@@ -133,6 +133,7 @@ public extension AdditiveArithmetic where Self : ExpressibleByIntegerLiteral {
   ///
   /// Zero is the identity element for addition. For any value,
   /// `x + .zero == x` and `.zero + x == x`.
+  @_transparent
   static var zero: Self {
     return 0
   }