Use new &raw feature for sound raw pointer usage.

Note: this requires Rust 1.82.0.

listings/ch20-advanced-features/listing-20-01/src/main.rs

@@ -2,7 +2,7 @@ fn main() {
     // ANCHOR: here
     let mut num = 5;
 
-    let r1 = &num as *const i32;
-    let r2 = &mut num as *mut i32;
+    let r1 = &raw const num;
+    let r2 = &raw mut num;
     // ANCHOR_END: here
 }

listings/ch20-advanced-features/listing-20-03/src/main.rs

@@ -2,8 +2,8 @@ fn main() {
     // ANCHOR: here
     let mut num = 5;
 
-    let r1 = &num as *const i32;
-    let r2 = &mut num as *mut i32;
+    let r1 = &raw const num;
+    let r2 = &raw mut num;
 
     unsafe {
         println!("r1 is: {}", *r1);

src/ch20-01-unsafe-rust.md

@@ -101,6 +101,11 @@ Notice that we don’t include the `unsafe` keyword in this code. We can create
 raw pointers in safe code; we just can’t dereference raw pointers outside an
 unsafe block, as you’ll see in a bit.
 
+<!--
+  TODO: rewrite to not use `as` initially, but to show that it is another way to
+  do it where you *need* to work with integer values directly instead.
+-->
+
 We’ve created raw pointers by using `as` to cast an immutable and a mutable
 reference into their corresponding raw pointer types. Because we created them
 directly from references guaranteed to be valid, we know these particular raw
@@ -136,6 +141,8 @@ dereference operator `*` on a raw pointer that requires an `unsafe` block.
 Creating a pointer does no harm; it’s only when we try to access the value that
 it points at that we might end up dealing with an invalid value.
 
+<!-- TODO: again, update this to account for using `&raw` -->
+
 Note also that in Listing 20-1 and 20-3, we created `*const i32` and `*mut i32`
 raw pointers that both pointed to the same memory location, where `num` is
 stored. If we instead tried to create an immutable and a mutable reference to