Add Unicode v15.1.0-sensitive `IdentifierPart` tests (#3833)

Ref. https://github.com/tc39/ecma262/issues/3073

test/language/identifiers/part-unicode-15.1.0-class-escaped.js

@@ -0,0 +1,20 @@
+// Copyright 2023 Mathias Bynens. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+author: Mathias Bynens
+esid: prod-PrivateIdentifier
+description: |
+  Test that Unicode v15.1.0 ID_Continue characters are accepted as
+  identifier part characters in escaped form, i.e.
+  - \uXXXX or \u{XXXX} for BMP symbols
+  - \u{XXXXXX} for astral symbols
+  in private class fields.
+info: |
+  Generated by https://github.com/mathiasbynens/caniunicode
+features: [class, class-fields-private]
+---*/
+
+class _ {
+  #_\u200C\u200D;
+};

test/language/identifiers/part-unicode-15.1.0-class.js

@@ -0,0 +1,17 @@
+// Copyright 2023 Mathias Bynens. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+author: Mathias Bynens
+esid: prod-PrivateIdentifier
+description: |
+  Test that Unicode v15.1.0 ID_Continue characters are accepted as
+  identifier part characters in private class fields.
+info: |
+  Generated by https://github.com/mathiasbynens/caniunicode
+features: [class, class-fields-private]
+---*/
+
+class _ {
+  #_‌‍;
+};

test/language/identifiers/part-unicode-15.1.0-escaped.js

@@ -0,0 +1,16 @@
+// Copyright 2023 Mathias Bynens. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+author: Mathias Bynens
+esid: sec-names-and-keywords
+description: |
+  Test that Unicode v15.1.0 ID_Continue characters are accepted as
+  identifier part characters in escaped form, i.e.
+  - \uXXXX or \u{XXXX} for BMP symbols
+  - \u{XXXXXX} for astral symbols
+info: |
+  Generated by https://github.com/mathiasbynens/caniunicode
+---*/
+
+var _\u200C\u200D;

test/language/identifiers/part-unicode-15.1.0.js

@@ -0,0 +1,14 @@
+// Copyright 2023 Mathias Bynens. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+author: Mathias Bynens
+esid: sec-names-and-keywords
+description: |
+  Test that Unicode v15.1.0 ID_Continue characters are accepted as
+  identifier part characters.
+info: |
+  Generated by https://github.com/mathiasbynens/caniunicode
+---*/
+
+var _‌‍;