Simplify Debug display of DebugName (bevyengine#21870)

# Objective

As noted in bevyengine#21856, the `Debug` output of `DebugName` is too verbose. It
is supposed to be a thin wrapper around a string, but it renders as a
`struct`.

## Solution

Manually `impl Debug for DebugName` and write the string directly.  

## Showcase

The following code

```rust
#[derive(Debug)]
struct TestStruct {
    debug_name: DebugName,
}
let test_struct = TestStruct {
    debug_name: DebugName::type_name::<TestStruct>(),
};
println!("{test_struct:#?}");
```

Prints the following before this change

```
TestStruct {
    debug_name: DebugName {
        name: "crate_name::TestStruct",
    },
}
```

And the following after it

```
TestStruct {
    debug_name: "crate_name::TestStruct",
}
```

When the `debug` feature is disabled, it prints the following both
before and after the change

```
TestStruct {
    debug_name: DebugName,
}
```

---------

Co-authored-by: François Mockers <[email protected]>

Author: 2 people

crates/bevy_utils/src/debug_info.rs

@@ -14,7 +14,7 @@ const FEATURE_DISABLED: &str = "Enable the debug feature to see the name";
 ///
 /// * If the `debug` feature is enabled, the actual name will be used
 /// * If it is disabled, a string mentioning the disabled feature will be used
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, PartialEq, Eq)]
 pub struct DebugName {
     #[cfg(feature = "debug")]
     name: Cow<'static, str>,
@@ -23,12 +23,15 @@ pub struct DebugName {
 cfg::alloc! {
     impl fmt::Display for DebugName {
         fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-            #[cfg(feature = "debug")]
-            f.write_str(self.name.as_ref())?;
-            #[cfg(not(feature = "debug"))]
-            f.write_str(FEATURE_DISABLED)?;
+            // Deref to `str`, which will use `FEATURE_DISABLED` if necessary
+            write!(f, "{}", &**self)
+        }
+    }
 
-            Ok(())
+    impl fmt::Debug for DebugName {
+        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+            // Deref to `str`, which will use `FEATURE_DISABLED` if necessary
+            write!(f, "{:?}", &**self)
         }
     }
 }