Difficult to query for a specific AnimationPlayer

## Bevy version

0.12, main

## What you did

1. Load multiple gltf files with animations (Fox.glb and Bear.glb for example)
2. Spawn them using SceneBundle and marker components Fox and Bear
3. Query for the AnimationPlayer like in the animated_fox example, but try to query for a specific AnimationPlayer. So `mut animation_players: Query<&mut AnimationPlayer, With>,`

## What went wrong

The query is empty. This is because the AnimationPlayer does not get spawned at the top-level entity (understandably). However, this is not clear from the example or the documentation as far as I could see.

It would be nice to make sure this is clear in the examples/documentation and/or provide the user with something that would make this easy to work around. The current workaround (see links below) is not very user friendly, or maybe I haven't found the right methods yet.

## Additional information

I haven't used multiple animations before but these users (bless them) ran into this issue just this week:
https://discord.com/channels/691052431525675048/1204798006591881216/1204824802725068851
https://discord.com/channels/691052431525675048/1202378612251037776/1202378612251037776