Fix reflected serialization/deserialization on Name component

[coreh]

Objective

• This PR makes it so that ReflectSerialize and ReflectDeserialize traits are properly derived on Name. This avoids having the internal hash “leak” into the serialization when using reflection.

Solution

• Added a conditional derive for ReflectDeserialize and ReflectSerialize via #[cfg_attr()]

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Changelog

• Name now correctly implements ReflectDeserialize and ReflectSerialize whenever the serialize feature is enabled.

Migration Guide

• Existing scene files containing the former (incorrect) serialization of the Name component will require patching. Search for bevy_core::name::Name, and replace the following structure ( "name": "My Entity Name", "hash": ... ) with just a string: "My Entity Name".

[MrGVSV]

Since this is technically a breaking change (i.e. existing scenes could now be invalid and/or expectations of what's included in the serialized output), could you add a migration guide?

[github-actions]

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Could you add some context on what users should update when this change get released in a new version of Bevy?
It will be used to help writing the migration guide for the version. Putting it after a ## Migration Guide will help it get automatically picked up by our tooling.

[coreh]

Since this is technically a breaking change (i.e. existing scenes could now be invalid and/or expectations of what's included in the serialized output), could you add a migration guide?

Just saw this now, but the PR is already merged. 😕 Are we using the reflection (de)serialization for scenes? In this case I can add an entry to the migration guide, will the release script still pick it up even after the PR is merged? Will we need to include it manually later when writing the notes?

[MrGVSV]

Are we using the reflection (de)serialization for scenes?

Yep! It's what powers the scene system essentially.

In this case I can add an entry to the migration guide, will the release script still pick it up even after the PR is merged? Will we need to include it manually later when writing the notes?

I believe the script is only run towards the end of the cycle. So it should pick it up if you add it now.

[coreh]

@MrGVSV Ended up adding backwards compatibility to the old format: #11485

This should give people time to more easily migrate.

Edit: That turned out to be problematic due to non-self-describing serialization format compatibility. Just adding a migration guide instead.

[Testare]

This doesn't seem to be working in 0.13?

https://discord.com/channels/691052431525675048/1019697973933899910/threads/1209244908372627507