Auto merge of #88865 - guswynn:must_not_suspend, r=oli-obk

Implement `#[must_not_suspend]`

implements #83310

Some notes on the impl:

1. The code that searches for the attribute on the ADT is basically copied from the `must_use` lint. It's not shared, as the logic did diverge
2. The RFC does specify that the attribute can be placed on fn's (and fn-like objects), like `must_use`. I think this is a direct copy from the `must_use` reference definition. This implementation does NOT support this, as I felt that ADT's (+ `impl Trait` + `dyn Trait`) cover the usecase's people actually want on the RFC, and adding an imp for the fn call case would be significantly harder. The `must_use` impl can do a single check at fn call stmt time, but `must_not_suspend` would need to answer the question: "for some value X with type T, find any fn call that COULD have produced this value". That would require significant changes to `generator_interior.rs`, and I would need mentorship on that. `@eholk` and I are discussing it.
3. `@estebank` do you know a way I can make the user-provided `reason` note pop out? right now it seems quite hidden

Also, I am not sure if we should run perf on this

r? `@nikomatsakis`

compiler/rustc_feature/src/active.rs

@@ -675,6 +675,10 @@ declare_features! (
     /// Allows `let...else` statements.
     (active, let_else, "1.56.0", Some(87335), None),
 
+    /// Allows the `#[must_not_suspend]` attribute.
+    (active, must_not_suspend, "1.57.0", Some(83310), None),
+
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------