Add new test files for OEMCrypto v17.2

The previous commit did not include some new files.

util/include/string_format.h

@@ -0,0 +1,18 @@
+// Copyright 2022 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine License
+// Agreement.
+#ifndef WVCDM_UTIL_STRING_FORMAT_H_
+#define WVCDM_UTIL_STRING_FORMAT_H_
+
+#include <string>
+
+namespace wvutil {
+
+#ifdef __GNUC__
+[[gnu::format(printf, 2, 3)]]
+#endif
+bool FormatString(std::string* out, const char* fmt, ...);
+
+}  // namespace wvutil
+
+#endif  // WVCDM_UTIL_STRING_FORMAT_H_