Add load_untyped to LoadContext

[Testare]

Objective

Give us the ability to load untyped assets in AssetLoaders.

Solution

Basically just copied the code from load, but used asset_server.load_untyped instead internally.

Changelog

Added load_untyped method to LoadContext

[Testare]

Failing test doesn't seem to be related to this change.

Have also via Cargo.toml [patch] have been able to confirm it works just fine for me. Please consider this for a 12.x release =]

[cart]

I'm on board for this / the code is correct, but I do wonder about the utility of exposing this to AssetLoaders, as it would imply you are loading handles in assets that must later be resolved to the "final handle" by consumers of the asset.

[Testare]

Thank you for taking the time to review/approve and merge!

If you want to know, my use case is I have custom ".bam(.txt)" files, or "Bevy Asset Manifest" assets. They are simple lists of different assets I want loaded together. In this case, the BAM asset itself doesn't really care about what the thing is that is being loaded, just that it is loaded. This triggers the asset event listeners that DO care about what is loaded (I have some assets that essentially only exist to be loaded and fed into a common resource), as well as allowing me to specify a bundle of assets to be "preloaded."