Log an error when registering an AssetSource after AssetPlugin has be…

…en built (#10202)

# Objective

- Provides actionable feedback when users encounter the error in
#10162
- Complements #10186

## Solution

- Log an error when registering an AssetSource after the AssetPlugin has
been built (via DefaultPlugins). This will let users know that their
registration order needs changing

The outputted error message will look like this:
```rust
ERROR bevy_asset::server: 'AssetSourceId::Name(test)' must be registered before `AssetPlugin` (typically added as part of `DefaultPlugins`)
```

---------

Co-authored-by: 66OJ66 <[email protected]>
Co-authored-by: Alice Cecile <[email protected]>

crates/bevy_asset/src/lib.rs

@@ -47,6 +47,7 @@ use bevy_ecs::{
     schedule::{IntoSystemConfigs, IntoSystemSetConfigs, ScheduleLabel, SystemSet},
     world::FromWorld,
 };
+use bevy_log::error;
 use bevy_reflect::{FromReflect, GetTypeRegistration, Reflect, TypePath};
 use std::{any::TypeId, sync::Arc};
 
@@ -349,6 +350,11 @@ impl AssetApp for App {
         id: impl Into<AssetSourceId<'static>>,
         source: AssetSourceBuilder,
     ) -> &mut Self {
+        let id = id.into();
+        if self.world.get_resource::<AssetServer>().is_some() {
+            error!("{} must be registered before `AssetPlugin` (typically added as part of `DefaultPlugins`)", id);
+        }
+
         {
             let mut sources = self
                 .world