Use Asset Path Extension for AssetLoader Disambiguation (#11644)

# Objective

- Fixes #11638
- See
[here](#11638 (comment))
for details on the cause of this issue.

## Solution

- Modified `AssetLoaders` to capture possibility of multiple
`AssetLoader` registrations operating on the same `Asset` type, but
different extensions.
- Added an algorithm which will attempt to resolve via `AssetLoader`
name, then `Asset` type, then by extension. If at any point multiple
loaders fit a particular criteria, the next criteria is used as a tie
breaker.

crates/bevy_asset/src/loader.rs

@@ -38,6 +38,7 @@ pub trait AssetLoader: Send + Sync + 'static {
     ) -> BoxedFuture<'a, Result<Self::Asset, Self::Error>>;
 
     /// Returns a list of extensions supported by this [`AssetLoader`], without the preceding dot.
+    /// Note that users of this [`AssetLoader`] may choose to load files with a non-matching extension.
     fn extensions(&self) -> &[&str] {
         &[]
     }