Rollup merge of #52316 - seanmonstar:waker-unsafety, r=cramertj
task: remove wrong comments about non-existent LocalWake trait ~~A `LocalWaker` is specifically `!Send `, and the unsafety comment around `LocalWaker::new` only specifies that it be safe to call `wake_local`. One could then accidentally promote a `LocalWaker` into a `Waker`, which is universally `Send`, simply via `Waker::from(local_waker)`. A `LocalWaker` the was built expecting to not be `Send`, such as using `Rc`, could be sent to other threads safely.~~ ~~Separately, though somewhat related, `Context` holds a `&LocalWaker` internally, and exposes a `waker() -> &Waker` method. This simply transmutes the `&LocalWaker` to `&Waker`, which would be unsound, except that you can't "send" a `&Waker`, you'd need to clone it first. Since `UnsafeWake::clone_raw` requires that it return a `Waker`, the transmute is not unsound. The transmuted `LocalWaker` will be promoted to a `Waker` correctly.~~ ~~That would mean that if `UnsafeWake::clone_raw` were to be changed, such as returning `Self` instead of `Waker`, this would no longer be sound. Thus, this also adds a comment to `clone_raw` to remember this.~~ r? @cramertj
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