Hxcpp native format is always utf8, whether or not string length refers the characters or bytes

tests/unit/src/unitstd/Unicode.unit.hx

@@ -102,7 +102,7 @@ str.toHex() == "c3a9e38182f09f9882";
 
 var rawBytes = haxe.io.Bytes.ofString("éあ😂",RawNative);
 
-#if !utf16
+#if (!utf16 || cpp)
 rawBytes.toHex() == "c3a9e38182f09f9882"; // UTF-8 native
 #else
 rawBytes.toHex() == "e90042303dd802de"; // UTF-16 native