Additional tests for QuantifiableAssertion

- Tests that lookahead and lookbehind are not extended to
  QuantifiableAssertion, as in https://github.com/tc39/ecma262/pull/1102
- Additional tests verifying some more combinations of cases for
  QuantifiableAssertion being invalid in Unicode mode.

Based on the tests in https://chromium-review.googlesource.com/c/v8/v8/+/926102

These tests pass on V8 (if the throw for early errors is removed to
work around a V8 issue where RegExps don't have early errors).

test/language/literals/regexp/invalid-optional-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<=.)?/;

test/language/literals/regexp/invalid-optional-negative-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<!.)?/;

test/language/literals/regexp/invalid-range-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<=.){2,3}/;

test/language/literals/regexp/invalid-range-negative-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<!.){2,3}/;

test/language/literals/regexp/u-invalid-optional-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<=.)?/u;

test/language/literals/regexp/u-invalid-optional-negative-lookahead.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+es6id: B.1.4
+description: Quantifiable assertions disallowed with `u` flag
+info: |
+    The `u` flag precludes quantifiable assertions (even when Annex B is
+    honored)
+
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?!.)?/u;

test/language/literals/regexp/u-invalid-optional-negative-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<!.)?/u;

test/language/literals/regexp/u-invalid-range-lookahead.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+es6id: B.1.4
+description: Quantifiable assertions disallowed with `u` flag
+info: |
+    The `u` flag precludes quantifiable assertions (even when Annex B is
+    honored)
+
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?=.){2,3}/u;

test/language/literals/regexp/u-invalid-range-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<=.){2,3}/u;

test/language/literals/regexp/u-invalid-range-negative-lookahead.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+es6id: B.1.4
+description: Quantifiable assertions disallowed with `u` flag
+info: |
+    The `u` flag precludes quantifiable assertions (even when Annex B is
+    honored)
+
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?!.){2,3}/u;

test/language/literals/regexp/u-invalid-range-negative-lookbehind.js

+// Copyright (C) 2018 Igalia S. L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-regular-expressions-patterns
+description: Lookbehinds are not treated as a QuantifiableAssertion
+info: |
+    Term[U] ::
+         [~U] QuantifiableAssertion Quantifier
+
+    QuantifiableAssertion[N]::
+        ( ? = Disjunction[~U, ?N] )
+        ( ? ! Disjunction[~U, ?N] )
+negative:
+  phase: parse
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+/.(?<!.){2,3}/u;