base: Add JSON string non-ASCII escaping options

- Add HEIM_JSON_F_ESCAPE_NON_ASCII to indicate that non-ASCII must be
   escaped as \uXXXX.

 - Add HEIM_JSON_F_NO_ESCAPE_NON_ASCII to force non-escaping of BMP
   codepoints.

 - If the locale's codeset is not UTF-8 and
   HEIM_JSON_F_NO_ESCAPE_NON_ASCII is not set, then set
   HEIM_JSON_F_ESCAPE_NON_ASCII.

lib/base/version-script.map

@@ -148,6 +148,7 @@ HEIMDAL_BASE_1.0 {
 		heim_json_create_with_bytes;
 		heim_json_eq;
 		heim_load_plugins;
+		heim_locale_is_utf8;
 		heim_log;
 		heim_log_msg;
 		_heim_make_permanent;