[wasm][coreclr] Update contract of SystemJS_ExecuteFinalizationCallback

[radekdoulik]

After ManagedThreadBase::KickOff call was enabled again, the contract needs same treatment as in FinalizerThread::FinalizerThreadStart

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[Copilot]

Pull request overview

Updates the CoreCLR finalizer callback contract for Browser/WASM so it matches the exception-trap behavior used by FinalizerThread::FinalizerThreadStart, now that ManagedThreadBase::KickOff is used again in this path.

Changes:

• Adjust SystemJS_ExecuteFinalizationCallback’s CONTRACTL to be NOTHROW on TARGET_UNIX and THROWS otherwise, aligning with the existing finalizer thread entrypoint contract.

[Copilot]

In TARGET_BROWSER builds, TARGET_UNIX is always defined by the build (see clrdefinitions.cmake), so this #ifdef TARGET_UNIX/#else in the contract is effectively dead code and the inline comment about Windows is misleading in this context. Consider simplifying the contract to a single NOTHROW; (or otherwise keying off whether UNINSTALL_UNHANDLED_MANAGED_EXCEPTION_TRAP is active) to avoid an unreachable branch and reduce confusion.

Suggested change

	#ifdef TARGET_UNIX // because UNINSTALL_UNHANDLED_MANAGED_EXCEPTION_TRAP is catching exceptions only on Unix. On Windows OS is handling that.
	NOTHROW;
	#else // TARGET_UNIX
	THROWS;
	#endif // TARGET_UNIX
	NOTHROW;

[radekdoulik]

nm, copilot is right, we don't need this change