Update RegExp.prototype.{match,replace} tests to expect Get(rx, "flags")

[gibson042]

This adds tests for tc39/ecma262#2791 , which reached consensus at the July 2022 TC39 meeting.

[gibson042]

This results in failures, as expected:

results

FAIL test/built-ins/RegExp/prototype/Symbol.match/flags-tostring-error.js (default)
  Expected a CustomError but got a Test262Error

FAIL test/built-ins/RegExp/prototype/Symbol.match/get-flags-err.js (default)
  Expected a CustomError but got a Test262Error

FAIL test/built-ins/RegExp/prototype/Symbol.match/get-unicode-error.js (default)
  Expected a Test262Error to be thrown but no exception was thrown at all

FAIL test/built-ins/RegExp/prototype/Symbol.replace/flags-tostring-error.js (default)
  Expected a CustomError but got a Test262Error

FAIL test/built-ins/RegExp/prototype/Symbol.replace/get-flags-err.js (default)
  Expected a CustomError but got a Test262Error

FAIL test/built-ins/RegExp/prototype/Symbol.replace/get-unicode-error.js (default)
  Expected a Test262Error to be thrown but no exception was thrown at all

Do we have instructions for how to test such changes by modifying engine262?

[ptomato]

We don't have those instructions yet. That would be a great tutorial to have!

[gibson042]

@ptomato Do you have such experience? I don't, but I'd be happy to write something up from either a past example or a new pairing session.

[ptomato]

I don't either, and would love to learn. IIRC @devsnek once gave a demonstration of implementing a small proposal in engine262, so maybe they could help?

[devsnek]

@gibson042 maybe drop by https://matrix.to/#/#engine262:matrix.org and we can discuss? this should hopefully be quite straight-forward but i'd love to hear your feedback on the process.

[ljharb]

LGTM

[gibson042]

With help from @devsnek, I was able to verify that engine262 modifications to implement tc39/ecma262#2791 result in it passing all tests broken by this PR. 🎉