zxing-cpp: enable old and new writers

See https://github.com/zxing-cpp/zxing-cpp/releases/tag/v3.0.1
> It is generally advised for package maintainers to use the BOTH config option during the 3.0 release cycle to allow client applications (like e.g. LibreOffice) to work until they switch to the new API.

pkgs/by-name/zx/zxing-cpp/package.nix

@@ -38,6 +38,7 @@ stdenv.mkDerivation (finalAttrs: {
     "-DZXING_DEPENDENCIES=LOCAL"
     "-DZXING_EXAMPLES=OFF"
     "-DZXING_USE_BUNDLED_ZINT=OFF"
+    (lib.cmakeFeature "ZXING_WRITERS" "BOTH")
   ];
 
   passthru = {