[wasm] Add UTF-8 validation

src/unicode-inl.h

 // Copyright 2007-2010 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_UNICODE_INL_H_
 #define V8_UNICODE_INL_H_
 
 #include "src/unicode.h"
 #include "src/base/logging.h"
 #include "src/utils.h"
@@ skipping 119 matching lines @@
     if (Utf16::IsTrailSurrogate(c) &&
         Utf16::IsLeadSurrogate(previous)) {
       return kSizeOfUnmatchedSurrogate - kBytesSavedByCombiningSurrogates;
     }
     return 3;
   } else {
     return 4;
   }
 }
 
+bool Utf8::IsValidCharacter(uchar c) {
+  return c < 0xD800u || (c >= 0xE000u && c < 0xFDD0u) ||
+         (c > 0xFDEFu && c <= 0x10FFFFu && (c & 0xFFFEu) != 0xFFFEu &&
+          c != kBadChar);
+}
+
 }  // namespace unibrow
 
 #endif  // V8_UNICODE_INL_H_