The RegExp named groups specification has changed to not throw
errors in certain cases. This patch updates the test262 tests to match
the new specification, and throws in an additional test that verifies
the interaction between named group syntax and other replacement.
The tests pass on a version of V8 which implements the new semantics.

https://github.com/tc39/proposal-regexp-named-groups/commit/92ceba518c2ab0d2811c2efa8248ed1b3f8b5506

* Delete identifier-let-allowed-as-lefthandside-expression-non-strict.js

Fixes #1192

This is already covered by https://github.com/tc39/test262/blob/8422147c17aa3f4061e524a8f88c251a3b371ecf/test/language/statements/for-in/head-lhs-let.js#L27

* restore for-in test

* Add missing generators feature flags

* Generate files

* Add generators flags

* fixup! Add generators flags

* additional BigInt JSON tests

* single quotes

* BigInt stringify order of steps

* Improve tests for BigInt.prototype.valueOf

* fixup! Improve tests for BigInt.prototype.valueOf

* fixup! Improve tests for BigInt.prototype.valueOf

* fixup! Improve tests for BigInt.prototype.valueOf

* BigInt valueOf tests

* add features from typeCoercion.js

As per https://github.com/tc39/ecma402/pull/160 the formatToParts.length is set to 1.

https://github.com/tc39/ecma262/pull/988 changes the iteration protocol
such that the "next" method is only loaded from the iterator object once
during the prologue of iteration, rather than during each step.

Fixes #1202

* typeCoercion.js supports ToIndex
* typeCoercion.js supports ToBigInt
* updated BigInt.asIntN type coercion tests to use typeCoercion.js

Tests for ECMA 402 PR https://github.com/tc39/ecma402/pull/170
The tests on Date/DateTimeFormat are valid without the PR.