Make names of closure systems changable (#14369)

# Objective

When using tracing or
[`bevy_mod_debugdump`](https://github.com/jakobhellermann/bevy_mod_debugdump),
the names of function systems produced by closures are either ambiguous
(like `game::mainapp::{closure}` when tracing) or too long
(`bevy_mod_debugdump` includes full type signature if no name given),
which makes debugging with tracing difficult.

## Solution
Add a function `with_name` to rename a system. The proposed API can be
used in the following way:
```rust
app
    .add_systems(Startup, IntoSystem::into_system(|name: SystemName| {
        println!("System name: {}", name.name().to_owned());
    }).with_name("print_test_system"));
```

## Testing
- There is a test in
`bevy_ecs::system:system_name::test_closure_system_name_regular_param`

crates/bevy_ecs/src/system/exclusive_function_system.rs

@@ -30,6 +30,19 @@ where
     marker: PhantomData<fn() -> Marker>,
 }
 
+impl<Marker, F> ExclusiveFunctionSystem<Marker, F>
+where
+    F: ExclusiveSystemParamFunction<Marker>,
+{
+    /// Return this system with a new name.
+    ///
+    /// Useful to give closure systems more readable and unique names for debugging and tracing.
+    pub fn with_name(mut self, new_name: impl Into<Cow<'static, str>>) -> Self {
+        self.system_meta.set_name(new_name.into());
+        self
+    }
+}
+
 /// A marker type used to distinguish exclusive function systems from regular function systems.
 #[doc(hidden)]
 pub struct IsExclusiveFunctionSystem;

crates/bevy_ecs/src/system/function_system.rs

@@ -56,6 +56,20 @@ impl SystemMeta {
         &self.name
     }
 
+    /// Sets the name of of this system.
+    ///
+    /// Useful to give closure systems more readable and unique names for debugging and tracing.
+    pub fn set_name(&mut self, new_name: impl Into<Cow<'static, str>>) {
+        let new_name: Cow<'static, str> = new_name.into();
+        #[cfg(feature = "trace")]
+        {
+            let name = new_name.as_ref();
+            self.system_span = info_span!("system", name = name);
+            self.commands_span = info_span!("system_commands", name = name);
+        }
+        self.name = new_name;
+    }
+
     /// Returns true if the system is [`Send`].
     #[inline]
     pub fn is_send(&self) -> bool {
@@ -422,6 +436,14 @@ where
             marker: PhantomData,
         }
     }
+
+    /// Return this system with a new name.
+    ///
+    /// Useful to give closure systems more readable and unique names for debugging and tracing.
+    pub fn with_name(mut self, new_name: impl Into<Cow<'static, str>>) -> Self {
+        self.system_meta.set_name(new_name.into());
+        self
+    }
 }
 
 // De-initializes the cloned system.

crates/bevy_ecs/src/system/system_name.rs

@@ -105,7 +105,7 @@ impl ExclusiveSystemParam for SystemName<'_> {
 
 #[cfg(test)]
 mod tests {
-    use crate::system::SystemName;
+    use crate::system::{IntoSystem, RunSystemOnce, SystemName};
     use crate::world::World;
 
     #[test]
@@ -131,4 +131,23 @@ mod tests {
         let name = world.run_system(id).unwrap();
         assert!(name.ends_with("testing"));
     }
+
+    #[test]
+    fn test_closure_system_name_regular_param() {
+        let mut world = World::default();
+        let system =
+            IntoSystem::into_system(|name: SystemName| name.name().to_owned()).with_name("testing");
+        let name = world.run_system_once(system);
+        assert_eq!(name, "testing");
+    }
+
+    #[test]
+    fn test_exclusive_closure_system_name_regular_param() {
+        let mut world = World::default();
+        let system =
+            IntoSystem::into_system(|_world: &mut World, name: SystemName| name.name().to_owned())
+                .with_name("testing");
+        let name = world.run_system_once(system);
+        assert_eq!(name, "testing");
+    }
 }