[regexp] Support unicode capture names in non-unicode patterns

test/mjsunit/harmony/regexp-named-captures.js

 // Copyright 2017 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.
 
 // Flags: --harmony-regexp-named-captures --harmony-regexp-lookbehind
 
 // Malformed named captures.
 assertThrows("/(?<>a)/u", SyntaxError);  // Empty name.
 assertThrows("/(?<aa)/u", SyntaxError);  // Unterminated name.
 assertThrows("/(?<42a>a)/u", SyntaxError);  // Name starting with digits.
@@ skipping 129 matching lines @@
 assertEquals("a", /(?<$𐒤>a)/u.exec("bab").groups.$𐒤);
 assertEquals("a", /(?<_\u200C>a)/u.exec("bab").groups._\u200C);
 assertEquals("a", /(?<_\u200D>a)/u.exec("bab").groups._\u200D);
 assertEquals("a", /(?<ಠ_ಠ>a)/u.exec("bab").groups.ಠ_ಠ);
 assertThrows('/(?<❤>a)/u', SyntaxError);
 assertThrows('/(?<𐒤>a)/u', SyntaxError);  // ID_Continue but not ID_Start.
 
 assertEquals("a", /(?<π>a)/.exec("bab").groups.π);
 assertEquals("a", /(?<$>a)/.exec("bab").groups.$);
 assertEquals("a", /(?<_>a)/.exec("bab").groups._);
-assertThrows("/(?<$𐒤>a)/", SyntaxError);
+assertEquals("a", /(?<$𐒤>a)/.exec("bab").groups.$𐒤);
 assertEquals("a", /(?<ಠ_ಠ>a)/.exec("bab").groups.ಠ_ಠ);
 assertThrows('/(?<❤>a)/', SyntaxError);
 assertThrows('/(?<𐒤>a)/', SyntaxError);  // ID_Continue but not ID_Start.
 
 // Interaction with lookbehind assertions.
 assertEquals(["f", "c"], "abcdef".match(/(?<=(?<a>\w){3})f/u));
 assertEquals({a: "c"}, "abcdef".match(/(?<=(?<a>\w){3})f/u).groups);
 assertEquals({a: "b"}, "abcdef".match(/(?<=(?<a>\w){4})f/u).groups);
 assertEquals({a: "a"}, "abcdef".match(/(?<=(?<a>\w)+)f/u).groups);
 assertNull("abcdef".match(/(?<=(?<a>\w){6})f/u));
@@ skipping 201 matching lines @@
 // named captures).
 {
   let re = toSlowMode(/(?<fst>.)(?<snd>.)/u);
   assertEquals("bacd", "abcd".replace(re, "$<snd>$<fst>"));
   assertEquals("bacd", "abcd".replace(re, "$2$1"));
   assertThrows(() => "abcd".replace(re, "$<snd"), SyntaxError);
   assertEquals("cd", "abcd".replace(re, "$<42$1>"));
   assertEquals("cd", "abcd".replace(re, "$<thd>"));
   assertEquals("cd", "abcd".replace(re, "$<$1>"));
 }