Rollup merge of rust-lang#57848 - jrvanwhy:transmute-export-doc, r=QuietMisdreavus

Generate a documentation page for core::mem::transmute.

In `#[no_std]` environments, `std::mem::transmute` is unavailable. Searching for "core transmute" online only pulls up `core::intrinsics::transmute`, which is behind the (unstable) `core_intrinsics` feature flag. Users wishing to use transmute in `#[no_std]` environments typically should use `core::mem::transmute` instead, as it is stable. This documentation makes `core::mem::transmute` discoverable.

Author: GuillaumeGomez

src/libcore/mem.rs

@@ -15,6 +15,7 @@ use ptr;
 use ops::{Deref, DerefMut};
 
 #[stable(feature = "rust1", since = "1.0.0")]
+#[doc(inline)]
 pub use intrinsics::transmute;
 
 /// Takes ownership and "forgets" about the value **without running its destructor**.