Rollup merge of rust-lang#84547 - RalfJung:max_const_fn, r=oli-obk

Get rid of is_min_const_fn

This removes the last trace of the min_const_fn mechanism by making the unsafety checker agnostic about whether something is a min or "non-min" const fn. It seems this distinction was used to disallow some features inside `const fn`, but that is the responsibility of the const checker, not of the unsafety checker. No test seems to even notice this change in the unsafety checker so I guess we are good...

r? `@oli-obk`
Cc rust-lang#84510

Author: Dylan-DPC

Diff for: alloc/src/raw_vec.rs

@@ -53,17 +53,11 @@ pub struct RawVec<T, A: Allocator = Global> {
 }
 
 impl<T> RawVec<T, Global> {
-    /// HACK(Centril): This exists because `#[unstable]` `const fn`s needn't conform
-    /// to `min_const_fn` and so they cannot be called in `min_const_fn`s either.
+    /// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
+    /// they cannot call `Self::new()`.
     ///
-    /// If you change `RawVec<T>::new` or dependencies, please take care to not
-    /// introduce anything that would truly violate `min_const_fn`.
-    ///
-    /// NOTE: We could avoid this hack and check conformance with some
-    /// `#[rustc_force_min_const_fn]` attribute which requires conformance
-    /// with `min_const_fn` but does not necessarily allow calling it in
-    /// `stable(...) const fn` / user code not enabling `foo` when
-    /// `#[rustc_const_unstable(feature = "foo", issue = "01234")]` is present.
+    /// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
+    /// that would truly const-call something unstable.
     pub const NEW: Self = Self::new();
 
     /// Creates the biggest possible `RawVec` (on the system heap)