Test parsing error when using unicode escape sequences to express i, …

…m, s

As suggested in #3960 (comment)

test/language/literals/regexp/early-err-modifiers-should-not-unicode-escape-i.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Source text cannot use unicode escape sequences to express code points "i", "m", "s" (regular expression flags)
+esid: sec-patterns-static-semantics-early-errors
+features: [regexp-modifiers]
+negative:
+  phase: parse
+  type: SyntaxError
+info: |
+    Atom :: ( ? RegularExpresisonFlags : Disjunction )
+    It is a Syntax Error if the source text matched by RegularExpressionFlags contains any code points other than "i", "m", "s", or if it contains the same code point more than once.
+
+---*/
+
+$DONOTEVALUATE();
+
+/(?\u0069:a)/u /* i */;

test/language/literals/regexp/early-err-modifiers-should-not-unicode-escape-m.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Source text cannot use unicode escape sequences to express code points "i", "m", "s" (regular expression flags)
+esid: sec-patterns-static-semantics-early-errors
+features: [regexp-modifiers]
+negative:
+  phase: parse
+  type: SyntaxError
+info: |
+    Atom :: ( ? RegularExpresisonFlags : Disjunction )
+    It is a Syntax Error if the source text matched by RegularExpressionFlags contains any code points other than "i", "m", "s", or if it contains the same code point more than once.
+
+---*/
+
+$DONOTEVALUATE();
+
+/(?\u006D:a)/u /* m */;

test/language/literals/regexp/early-err-modifiers-should-not-unicode-escape-s.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Source text cannot use unicode escape sequences to express code points "i", "m", "s" (regular expression flags)
+esid: sec-patterns-static-semantics-early-errors
+features: [regexp-modifiers]
+negative:
+  phase: parse
+  type: SyntaxError
+info: |
+    Atom :: ( ? RegularExpresisonFlags : Disjunction )
+    It is a Syntax Error if the source text matched by RegularExpressionFlags contains any code points other than "i", "m", "s", or if it contains the same code point more than once.
+
+---*/
+
+$DONOTEVALUATE();
+
+/(?\u0073:a)/u /* s */;