Fix inconsistency between Debug and serialized representation of Enti…

…ty (#12469)

# Objective

Fixes #12139 

## Solution

- Derive `Debug` impl for `Entity`
- Add impl `Display` for `Entity`
- Add `entity_display` test to check the output contains all required
info

I decided to go with `0v0|1234` format as opposed to the `0v0[1234]`
which was initially discussed in the issue.

My rationale for this is that `[1234]` may be confused for index values,
which may be common in logs, and so searching for entities by text would
become harder. I figured `|1234` would help the entity IDs stand out
more.

Additionally, I'm a little concerned that this change is gonna break
existing logging for projects because `Debug` is now going to be a
multi-line output. But maybe this is ok.

We could implement `Debug` to be a single-line output, but then I don't
see why it would be different from `Display` at all.

@alice-i-cecile Let me know if we'd like to make any changes based on
these points.

crates/bevy_ecs/src/entity/mod.rs

@@ -139,7 +139,7 @@ type IdCursor = isize;
 /// [`Query::get`]: crate::system::Query::get
 /// [`World`]: crate::world::World
 /// [SemVer]: https://semver.org/
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 #[cfg_attr(feature = "bevy_reflect", derive(Reflect))]
 #[cfg_attr(
     feature = "bevy_reflect",
@@ -384,9 +384,15 @@ impl<'de> Deserialize<'de> for Entity {
     }
 }
 
-impl fmt::Debug for Entity {
+impl fmt::Display for Entity {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}v{}", self.index(), self.generation())
+        write!(
+            f,
+            "{}v{}|{}",
+            self.index(),
+            self.generation(),
+            self.to_bits()
+        )
     }
 }
 
@@ -1147,4 +1153,14 @@ mod tests {
             assert_ne!(hash, first_hash);
         }
     }
+
+    #[test]
+    fn entity_display() {
+        let entity = Entity::from_raw(42);
+        let string = format!("{}", entity);
+        let bits = entity.to_bits().to_string();
+        assert!(string.contains("42"));
+        assert!(string.contains("v1"));
+        assert!(string.contains(&bits));
+    }
 }