add unitxt encode/decode actions

src/UnicodeTextSet.hh

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+std::vector<std::u16string> parse_unicode_text_set(const std::string& prs_data);
+std::string serialize_unicode_text_set(const std::vector<std::u16string>& strings);