[libfuzzer] moving icu fuzzers to //third_party/icu, additional fuzzers.

fuzzers/icu_uregex_open_fuzzer.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "third_party/icu/source/i18n/unicode/regex.h"
+
+// Entry point for LibFuzzer.
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  UParseError pe = { 0 };
+  UErrorCode status = U_ZERO_ERROR;
+  URegularExpression* re = uregex_open(reinterpret_cast<const UChar*>(data),
+                                       static_cast<int>(size) / sizeof(UChar),
+                                       0, &pe, &status);
+  if (re)
+    uregex_close(re);
+
+  return 0;
+}