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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[rust-log-analyzer]

The job aarch64-gnu-llvm-20-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

296    |
297    = help: `#[rustc_force_inline]` can only be applied to functions
298 
- error: attribute cannot be applied to a `async`, `gen` or `async gen` function
-   --> $DIR/invalid.rs:135:1
-    |
- LL | #[rustc_force_inline]
-    | ^^^^^^^^^^^^^^^^^^^^^
- LL |
- LL | async fn async_foo() {}
-    | -------------------- `async`, `gen` or `async gen` function
- 
- error: attribute cannot be applied to a `async`, `gen` or `async gen` function
-   --> $DIR/invalid.rs:139:1
-    |
- LL | #[rustc_force_inline]
-    | ^^^^^^^^^^^^^^^^^^^^^
- LL |
- LL | gen fn gen_foo() {}
-    | ---------------- `async`, `gen` or `async gen` function
- 
- error: attribute cannot be applied to a `async`, `gen` or `async gen` function
-   --> $DIR/invalid.rs:143:1
-    |
- LL | #[rustc_force_inline]
-    | ^^^^^^^^^^^^^^^^^^^^^
- LL |
- LL | async gen fn async_gen_foo() {}
-    | ---------------------------- `async`, `gen` or `async gen` function
- 
- error: aborting due to 36 previous errors
+ error: aborting due to 33 previous errors
327 
328 Some errors have detailed explanations: E0539, E0805.
---
To only update this specific test, also pass `--test-args force-inlining/invalid.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/force-inlining/invalid.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/force-inlining/invalid" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2024"
stdout: none
--- stderr -------------------------------
error: allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes in function parameters
##[error]  --> /checkout/tests/ui/force-inlining/invalid.rs:131:11
   |
LL | fn barqux(#[rustc_force_inline] _x: u32) {}
   |           ^^^^^^^^^^^^^^^^^^^^^

error[E0805]: malformed `rustc_force_inline` attribute input
##[error]  --> /checkout/tests/ui/force-inlining/invalid.rs:15:1
   |
LL | #[rustc_force_inline(bar, baz)]
   | ^^^^^^^^^^^^^^^^^^^^----------^
   |                     |
   |                     expected a single argument here
   |
help: try changing it to one of the following valid forms of the attribute
   |
LL - #[rustc_force_inline(bar, baz)]
LL + #[rustc_force_inline = "reason"]
   |
LL - #[rustc_force_inline(bar, baz)]
LL + #[rustc_force_inline(reason)]
   |
LL - #[rustc_force_inline(bar, baz)]
LL + #[rustc_force_inline]
   |

error[E0539]: malformed `rustc_force_inline` attribute input
##[error]  --> /checkout/tests/ui/force-inlining/invalid.rs:20:1
   |
---
   |
LL - #[rustc_force_inline(2)]
LL + #[rustc_force_inline = "reason"]
   |
LL - #[rustc_force_inline(2)]
LL + #[rustc_force_inline(reason)]
   |
LL - #[rustc_force_inline(2)]
LL + #[rustc_force_inline]
   |

---
   |
LL - #[rustc_force_inline = 2]
LL + #[rustc_force_inline = "reason"]
   |
LL - #[rustc_force_inline = 2]
LL + #[rustc_force_inline(reason)]
   |
LL - #[rustc_force_inline = 2]
LL + #[rustc_force_inline]
   |

---

error: `#[rustc_force_inline]` attribute cannot be used on function params
##[error]  --> /checkout/tests/ui/force-inlining/invalid.rs:72:10
   |
LL | enum Bar<#[rustc_force_inline] T> {
   |          ^^^^^^^^^^^^^^^^^^^^^
   |
   = help: `#[rustc_force_inline]` can only be applied to functions

error: `#[rustc_force_inline]` attribute cannot be used on enum variants
---

error: `#[rustc_force_inline]` attribute cannot be used on function params
##[error]  --> /checkout/tests/ui/force-inlining/invalid.rs:131:11
   |
LL | fn barqux(#[rustc_force_inline] _x: u32) {}
   |           ^^^^^^^^^^^^^^^^^^^^^
   |
   = help: `#[rustc_force_inline]` can only be applied to functions

error: `#[rustc_force_inline]` attribute cannot be used on closures
##[error]  --> /checkout/tests/ui/force-inlining/invalid.rs:148:14
   |
LL |     let _x = #[rustc_force_inline] || { };
   |              ^^^^^^^^^^^^^^^^^^^^^
   |
   = help: `#[rustc_force_inline]` can be applied to functions and inherent methods

error: `#[rustc_force_inline]` attribute cannot be used on expressions
##[error]  --> /checkout/tests/ui/force-inlining/invalid.rs:150:14
   |
LL |     let _y = #[rustc_force_inline] 3 + 4;
   |              ^^^^^^^^^^^^^^^^^^^^^
   |
   = help: `#[rustc_force_inline]` can only be applied to functions

error: `#[rustc_force_inline]` attribute cannot be used on statements