Make inline attributes apply to the generated poll in async fn

[xacrimon]

This PR adds lowering code (similar to how track_caller forwarding works) to async fn items and async || closures such that any inline attributes put on them are inherited by the generated coroutine (corresponding to the poll() implementation) and are not applied to the outer function. This behavior matches the accepted FCP in the first linked issue.

Code like the following now correctly codegen 3 functions

• async_fn_test::consumer
• async_fn_test::hi::{closure#0}
• core::ptr::drop_in_place::<async_fn_test::hi::{closure#0}>

#[inline(never)]
pub async fn hi() -> i32 {
    1337
}

pub fn consumer(cx: &mut Context<'_>) -> Option<i32> {
    let fut = hi();
    let pinned = pin!(fut);
    match pinned.poll(cx) {
        Poll::Ready(value) => Some(value),
        Poll::Pending => None,
    }
}

Fixes #129347 and fixes #106765.

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[JonathanBrouwer]

@rustbot author
CI is failing

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[bors]

☔ The latest upstream changes (presumably #149853) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-bors]

☔ The latest upstream changes made this pull request unmergeable. Please resolve the merge conflicts.

[Enselic]

Triage: Are you still working on this @xacrimon?

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.