Auto merge of #141348 - EFanZh:zero-cost-rc-deref, r=<try>

Make `Rc<T>::deref` zero-cost

This PR makes `Rc::deref` zero-cost by changing the internal pointer so that it points to the value directly instead of the allocation.

This is split out from #132553, which will also make `Arc::deref` zero-cost.

Author: bors

library/alloc/src/lib.rs

@@ -204,6 +204,8 @@
 #[macro_use]
 mod macros;
 
+#[cfg(not(no_rc))]
+mod raw_rc;
 mod raw_vec;
 
 // Heaps provided for low-level allocation strategies