V18.4.0 CAS plugin

Note that this version does not have Widevine Provisioning 4.0 support.
It is only suitable for device upgrades. A new patch with provisioning
4.0 support will be made later.

wvutil/include/string_format.h

@@ -0,0 +1,23 @@
+// 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, ...);
+
+#ifdef __GNUC__
+[[gnu::format(printf, 2, 0)]]
+#endif
+bool VFormatString(std::string* out, const char* fmt, va_list vlist);
+
+}  // namespace wvutil
+
+#endif  // WVCDM_UTIL_STRING_FORMAT_H_