[Intl] Fix RegExp [\W] with i flag

Add special condiction in
ecma262 #sec-runtime-semantics-canonicalize-ch Step 3.g-h.

Bug: chromium:971636
Change-Id: Id533beb66749af6e38ee114cf79f995a1156df20
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1652795Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62105}

src/regexp/jsregexp.cc

@@ -5963,7 +5963,15 @@ void CharacterRange::AddCaseEquivalents(Isolate* isolate, Zone* zone,
           upper2.toUpper(locale);
           // Only add if the upper case are the same.
           if (upper[0] == upper2[0]) {
-            others.add(start);
+            // #sec-runtime-semantics-canonicalize-ch
+            // 3.g. If the numeric value of ch ≥ 128 and the numeric value of
+            // cu < 128, return ch.
+            if (bottom >= 128 && start < 128) {
+              others.add(bottom);
+            } else {
+              // 3.h. 3.h. 3.h. Return cu.
+              others.add(start);
+            }
           }
           start++;
         }

test/intl/regress-971636.js

+// Copyright 2019 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.
+
+// Regression test about \W w/ i will match S
+
+assertEquals("RST", "RST".replace(/[\W_]/gi, ""));
+assertEquals("RST", "RST".replace(/[\W]/gi, ""));
+assertEquals("RST", "RST".replace(/[\Wa]/gi, ""));
+assertEquals(null, "s".match(/[\u00A0-\u0180]/i));