Refine C++ coroutine use

• Component: WebKit Misc.
• Status: RESOLVED FIXED

[Alex Christensen]

Task::promise_type::final_suspend() needs to return a std::experimental::suspend_always instead of a std::experimental::suspend_never, otherwise it crashes if we ever use co_return.  We don't yet, but we probably will.

ReceiveOperation and SendOperation inherit from std::experimental::suspend_never but override await_ready with an implementation more like std::experimental::suspend_always, and an await_suspend that actually does something interesting.  Instead of inheriting from std::experimental::suspend_never, just write out everything it does, which just requires adding an await_resume that returns void.

[Alex Christensen]

Pull request: https://github.com/WebKit/WebKit/pull/2297

[EWS]

Committed 252430@main (270e5776c43a): <https://commits.webkit.org/252430@main>

Reviewed commits have been landed. Closing PR #2297 and removing active labels.

[Radar WebKit Bug Importer]

<rdar://problem/96981634>