Tests for Thenable-curtailment

[mgaudet]

I just want to call out the commit message on c3386c6, esp. in light of #5115

These tests were authored with the assistance of an LLM, however they were
targeted and reviewed by myself.

The tests were validated on the prototype implemenation of SafePromiseResolve
in the Firefox tree; the tests highlight a current divergence between the
SpiderMonkey implementation and the spec-text as written (specfically
SpiderMonkey will currently defer on a then setter even with no getter,
which is not correct by specification).

(Of course, seeing that in the Github editor I realize how badly I typo'd some of that message 🤦 )

[github-actions]

32 new or modified tests were run on 7 engines.

View workflow run

Test results

Test	Engine262	GraalJS	JavaScriptCore	QuickJS	SpiderMonkey	V8	XS
built-ins/Promise/safe-resolve-promise/deferred-module-namespace.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-native-promise-pending-ticks.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-native-promise-ticks.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-object-prototype-then.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-proxy-empty-handler.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-proxy-get-trap.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-proxy-on-prototype-chain.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-proxy-revoked.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-self-resolution.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-call-throws.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-callable-own.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-callable-proto.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-deleted-before-job.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-getter-own.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-getter-proto.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-getter-throws.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-reject.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/deferred-then-this-binding.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/latch-after-deferred.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/latch-after-sync.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/latch-already-settled.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/latch-double-safe-resolve.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/latch-thenable-resolving-functions.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-no-then.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-non-object.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-null-proto-ignores-object-prototype-then.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-own-non-callable-then-shadows-callable.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-self-resolution.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-then-not-callable-proto.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-then-not-callable.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-then-setter-only-proto.js	❌	❌	❌	❌	❌	❌	❌
built-ins/Promise/safe-resolve-promise/sync-then-setter-only.js	❌	❌	❌	❌	❌	❌	❌

[mgaudet]

(See #5122 for the testing plan)