[await-dictionary] add failure case and edge case tests

[danialasaria]

Summary

This PR adds the remaining failure-case and edge-case coverage for the await-dictionary proposal's Promise keyed combinators:

• Promise.allKeyed
• Promise.allSettledKeyed

It follows the runtime/behavioral tests PR (#4932) and completes the testing plan from #4886.

What this PR covers

NewPromiseCapability failures (sync throws)

• Constructor body throws (ctx-ctor-throws.js)
• Executor does not provide callable resolve/reject in various combinations (capability-executor-not-callable.js)

GetPromiseResolve failures (async rejections)

• Get(constructor, "resolve") accessor throws (invoke-resolve-get-error-reject.js)
• Calling the resolved promiseResolve function throws (invoke-resolve-error-reject.js)

Invoke(then) failures (async rejections)

• Get(nextPromise, "then") accessor throws (invoke-then-get-error-reject.js)
• Calling nextPromise.then(...) throws (invoke-then-error-reject.js)

allKeyed rejection ordering

• Second promise to settle is rejected (reject-second.js)
• Last promise to settle is rejected (reject-last.js)

Synchronous thenables (step 8 edge case)

• Thenables that synchronously invoke onFulfilled during the loop, causing remainingElementsCount to reach zero before the loop exits (resolve-before-loop-exit.js)

Exotic object abrupt completions (Proxy)

• [[OwnPropertyKeys]] throws (ownkeys-throws.js)
• [[GetOwnProperty]] throws (getownproperty-throws.js)
• [[GetOwnProperty]] returns undefined -- key is skipped (getownproperty-returns-undefined.js)

Property descriptor filtering

• Non-enumerable keys are skipped (getownproperty-not-enumerable.js)

Notes

• All async tests use asyncTest from asyncHelpers.js per reviewer feedback on [await-dictionary] add runtime keyed Promise combinator tests #4932
• Sync tests use assert.throws(...)
• All tests are feature-gated with features: [await-dictionary]; Proxy tests additionally gate on Proxy
• Tests mirror existing patterns from Promise.all / Promise.allSettled test suites
• capability-executor-not-callable includes poisoned resolve getters (matching Promise.all counterpart) to detect wrong evaluation order

What this PR does not cover

This completes all items from the testing plan (#4886).

References

• Testing plan issue: Promise.allKeyed and Promise.allSettledKeyed testing plan #4886
• Prior runtime tests PR: [await-dictionary] add runtime keyed Promise combinator tests #4932
• Prior boilerplate PR: [await-dictionary] add boilerplate tests for Promise.allKeyed and Promise.allSettledKeyed #4927
• Proposal text: Await Dictionary

[acutmore]

Could we also have a test that a custom constructor is being 'constructed' rather than 'called'.

If we can use new.target we can check like:

var error = new Test262Error();
function Constructor(executor) {
  if (new.target !== Constructor) {
    throw error
  }
}

We can also have assertions that validate the arguments passed to a custom constructor are correct: should only be one argument: the executor. And it should be a function with length 2.

[acutmore]

Could we either move the callCount to after the assertions, or have a separate count for the start and end of the callback. Otherwise technically the assertions could reject and they are swallowed by the function caller yet the test would pass (unless the harness has some tracking logic to guarantee a test fails if a harness assertion errors, rather than relying on the exception bubbling up)