Require a `crate` field for every asset that is a crate

This will help determine an accurate "latest supported Bevy version" for every crate. Related issue: https://github.com/bevyengine/bevy-assets/issues/297.

Some assets have multiple crates, in which case any one of them can be used.

Review the related issue #297 first, then inspect the repository's asset records to identify entries that represent crates. Add a `crate` field to every such asset, using any one crate where an asset has multiple; done means all crate assets have the field needed to determine the latest supported Bevy version.

Written by the indexing model from the issue text.