glTF labels: add enum to avoid misspelling and keep up-to-date list documented

[mockersf]

Objective

• Followup to Add docs to bevy_gltf about loading parts of a Gltf asset #13548
• It added a list of all possible labels to documentation. This seems hard to keep up and doesn't stop people from making spelling mistake

Solution

• Add an enum that can create all the labels possible, and encourage its use rather than manually typed labels

[alice-i-cecile]

Much nicer pattern: I really like this.

[IceSentry]

The from_asset(path) thing reads a little weird, it would be nice if the asset label was a postfix thing like the string labels are but I'm not sure how that would even be implemented. Maybe something like GltfPath::new(<path>).label(<GltAssetLabel>).

Anyway, not a huge deal, having the enum in place is definitely a good thing and makes it way more self documenting.

LGTM

[alice-i-cecile]

Maybe something like GltfPath::new().label().

I have a moderate preference for this syntax, but if you don't get to it by this weekend I'm merging this on Monday anyways.

[alice-i-cecile]

Great! I think this is impactful enough to have a small section in the release note.

[mockersf]

GltfPath::new(<path>).label(<GltAssetLabel>)

I didn't manage to have an impl of this that I like, with the fact that <path> is a Into<AssetPath<'a>>, <label> a Into<CowArc<'a, str>>, and that some things must be only for 'static

[IceSentry]

I didn't manage to have an impl of this that I like,

Well it was worth a try, but it's not a huge deal if there's no clean solution. I'm happy with the PR as is and if someone finds something cleaner in the future we can always change it.

[alice-i-cecile]

Thank you to everyone involved with the authoring or reviewing of this PR! This work is relatively important and needs release notes! Head over to bevyengine/bevy-website#1327 if you'd like to help out.