[vm] Update Irregexp to V8 commit 254cc758346f10be2a7e22e55d90d4defe9cad74.

Includes support for modifier spans and duplicate named capture groups.

Drops the flow graph implementation to ease maintenance.

TEST=corelib/regexp
Bug: https://github.com/dart-lang/sdk/issues/56573
Bug: https://github.com/dart-lang/sdk/issues/61337
Bug: https://github.com/dart-lang/sdk/issues/62349
Bug: https://github.com/dart-lang/sdk/issues/62708
Change-Id: I05640ba945a4fa5476e7ad463738f4f39d842c14
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/480121
Reviewed-by: Lasse Nielsen <lrn@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

tests/corelib/regexp/duplicate_named_capture_group_test.dart

@@ -0,0 +1,34 @@
+// Copyright (c) 2026, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "package:expect/expect.dart";
+
+void main() {
+  var r = RegExp(r"0x(?<digits>[a-f0-9]+)|(?<digits>\d+)");
+
+  var m = r.firstMatch("0xabc")!;
+  Expect.equals(2, m.groupCount);
+  Expect.listEquals(["digits"], [...m.groupNames]);
+  Expect.equals("abc", m.namedGroup("digits"));
+  Expect.equals("abc", m[1]);
+  Expect.isNull(m[2]);
+
+  m = r.firstMatch("123")!;
+  Expect.equals(2, m.groupCount);
+  Expect.listEquals(["digits"], [...m.groupNames]);
+  Expect.equals("123", m.namedGroup("digits"));
+  Expect.isNull(m[1]);
+  Expect.equals("123", m[2]);
+
+  r = RegExp(r"(?<unmatched>A)|(?<unmatched>B)|(?<matched>C)|(?<matched>D)");
+  m = r.firstMatch("D")!;
+  Expect.equals(4, m.groupCount);
+  Expect.listEquals(["unmatched", "matched"], [...m.groupNames]);
+  Expect.isNull(m.namedGroup("unmatched"));
+  Expect.equals("D", m.namedGroup("matched"));
+  Expect.isNull(m[1]);
+  Expect.isNull(m[2]);
+  Expect.isNull(m[3]);
+  Expect.equals("D", m[4]);
+}

tests/corelib/regexp/group_modifier_test.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2026, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "package:expect/expect.dart";
+
+void main() {
+  var r = new RegExp(r"(?i:hello) world");
+  Expect.isTrue(r.hasMatch("hello world"));
+  Expect.isTrue(r.hasMatch("HELLO world"));
+  Expect.isFalse(r.hasMatch("hello WORLD"));
+  Expect.isFalse(r.hasMatch("HELLO WORLD"));
+
+  r = new RegExp(r"(?-i:hello) world", caseSensitive: false);
+  Expect.isTrue(r.hasMatch("hello world"));
+  Expect.isFalse(r.hasMatch("HELLO world"));
+  Expect.isTrue(r.hasMatch("hello WORLD"));
+  Expect.isFalse(r.hasMatch("HELLO WORLD"));
+}

tests/corelib/regexp/named_captures_2_test.dart

@@ -28,18 +28,16 @@
 
 import 'v8_regexp_utils.dart';
 
-// These test cases really belong in `named_captures_test` but they've been
-// broken out because they currently fail on all web backends.
 void main() {
-  assertThrows(() => RegExp(r"(?<$𐒤>a)"));
-  assertThrows(() => RegExp("(?<a\uD801\uDCA4>.)"));
-  assertThrows(() => RegExp(r"(?<a\uD801\uDCA4>.)"));
+  RegExp(r"(?<$𐒤>a)");
+  RegExp("(?<a\uD801\uDCA4>.)");
+  RegExp(r"(?<a\uD801\uDCA4>.)");
   assertThrows(() => RegExp("(?<a\uD801>.)"));
   assertThrows(() => RegExp(r"(?<a\uD801>.)"));
   assertThrows(() => RegExp("(?<a\uDCA4>.)"));
   assertThrows(() => RegExp(r"(?<a\uDCA4>.)"));
-  assertThrows(() => RegExp("(?<a\u{104A4}>.)"));
-  assertThrows(() => RegExp(r"(?<a\u{104A4}>.)"));
+  RegExp("(?<a\u{104A4}>.)");
+  RegExp(r"(?<a\u{104A4}>.)");
   assertThrows(() => RegExp("(?<a\u{10FFFF}>.)"));
   assertThrows(() => RegExp(r"(?<a\u{10FFFF}>.)"));
   assertThrows(() => RegExp(r"(?<a\\u{110000}>.)"));

tests/standalone/regress_52691_test.dart

@@ -5,7 +5,7 @@ void main() {
     var re = RegExp(r'[c-');
   } on FormatException catch (e, s) {
     Expect.equals(
-      "FormatException: Unterminated character class [c-",
+      "FormatException: Unterminated character class\n[c-",
       e.toString(),
     );
   }