Add conversion from DebugName to Cow<'static, str> (#21257)

# Objective

There seems to be no way to get the underlying `Cow<'static, str>` from
the `DebugName`.

This is useful for me to be able to use `DebugName` and have it interop
seamlessly with the `metrics` crate:
https://docs.rs/metrics/latest/metrics/type.SharedString.html

which is the standard why to register/record metrics in rust.

Is it possible to include this in 0.17?

---------

Co-authored-by: Alice Cecile <[email protected]>
Co-authored-by: Jan Hohenheim <[email protected]>

Author: 3 people

crates/bevy_utils/src/debug_info.rs

@@ -132,6 +132,26 @@ cfg::alloc! {
             Self::owned(value)
         }
     }
+
+    impl From<DebugName> for Cow<'static, str> {
+        #[cfg_attr(
+            not(feature = "debug"),
+            expect(
+                unused_variables,
+                reason = "The value will be ignored if the `debug` feature is not enabled"
+            )
+        )]
+        fn from(value: DebugName) -> Self {
+            #[cfg(feature = "debug")]
+            {
+                value.name
+            }
+            #[cfg(not(feature = "debug"))]
+            {
+                Cow::Borrowed(FEATURE_DISABLED)
+            }
+        }
+    }
 }
 
 impl From<&'static str> for DebugName {