[regexp] Fix unicode escapes in test strings

Some of these tests pass the pattern as a string, and in this case
there's a subtle distinction between

"/\u{0041}/"  // Unicode escape interpreted in string literal.

and

"/\\u{0041}/"  // Unicode escape interpreted by regexp parser.

Extend these tests to check both cases.

Thanks littledan@ for pointing this out.

BUG=v8:5437

Review-Url: https://codereview.chromium.org/2839923002
Cr-Commit-Position: refs/heads/master@{#44840}

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

@@ -195,10 +195,15 @@ assertTrue(/(?<\u0041>.)/u.test("a"));  // \u NonSurrogate
 assertTrue(/(?<\u{0041}>.)/u.test("a"));  // \u{ Non-surrogate }
 assertTrue(/(?<a\u{104A4}>.)/u.test("a"));  // \u{ Surrogate, ID_Continue }
 assertThrows("/(?<a\\u{110000}>.)/u", SyntaxError);  // \u{ Out-of-bounds }
+assertThrows("/(?<a\\uD801>.)/u", SyntaxError);  // Lead
+assertThrows("/(?<a\\uDCA4>.)/u", SyntaxError);  // Trail
 assertThrows("/(?<a\uD801>.)/u", SyntaxError);  // Lead
 assertThrows("/(?<a\uDCA4>.)/u", SyntaxError);  // Trail
+assertTrue(RegExp("(?<\\u{0041}>.)", "u").test("a"));  // Non-surrogate
+assertTrue(RegExp("(?<a\\u{104A4}>.)", "u").test("a"));  // Surrogate,ID_Continue
 assertTrue(RegExp("(?<\u{0041}>.)", "u").test("a"));  // Non-surrogate
 assertTrue(RegExp("(?<a\u{104A4}>.)", "u").test("a"));  // Surrogate,ID_Continue
+assertTrue(RegExp("(?<\\u0041>.)", "u").test("a"));  // Non-surrogate
 
 assertThrows("/(?<a\\uD801\uDCA4>.)/", SyntaxError);
 assertThrows("/(?<a\\uD801>.)/", SyntaxError);
@@ -207,10 +212,15 @@ assertTrue(/(?<\u0041>.)/.test("a"));
 assertThrows("/(?<\\u{0041}>.)/", SyntaxError);
 assertThrows("/(?<a\\u{104A4}>.)/", SyntaxError);
 assertThrows("/(?<a\\u{10FFFF}>.)/", SyntaxError);
+assertThrows("/(?<a\\uD801>.)/", SyntaxError);  // Lead
+assertThrows("/(?<a\\uDCA4>.)/", SyntaxError);  // Trail;
 assertThrows("/(?<a\uD801>.)/", SyntaxError);  // Lead
 assertThrows("/(?<a\uDCA4>.)/", SyntaxError);  // Trail
+assertThrows("/(?<\\u{0041}>.)/", SyntaxError);  // Non-surrogate
+assertThrows("/(?<a\\u{104A4}>.)/", SyntaxError);  // Surrogate, ID_Continue
 assertTrue(RegExp("(?<\u{0041}>.)").test("a"));  // Non-surrogate
 assertTrue(RegExp("(?<a\u{104A4}>.)").test("a"));  // Surrogate, ID_Continue
+assertTrue(RegExp("(?<\\u0041>.)").test("a"));  // Non-surrogate
 
 // @@replace with a callable replacement argument (no named captures).
 {