`EntityHashSet` doesn't seem to implement `Reflect` which seems weird!
Especially since `EntityHashMap` implements `Reflect`.
This PR just added an extra `impl_reflect_value!` for `EntityHashSet`
and this seems to do the trick.
I left out doing the same for `StableHashSet` since it's marked as
deprecated.
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I'm really wondering what was the issue here. If anyone can explain why
`EntityHashSet` can't use the `Reflect` impl of `bevy_utils::HashSet`
similar to how it's the case with the `...HashMap`s I'd be interested!