Make bevy_remote feature enable serialize feature

[mweatherley]

Objective

bevy_remote's reflection deserialization basically requires ReflectDeserialize registrations in order to work correctly. In the context of bevy (the library), this means that using bevy_remote without using the serialize feature is a footgun, since #[reflect(Serialize)] etc. are gated behind this feature.

The goal of this PR is to avoid this mistake by default.

Solution

Make the bevy_remote feature enable the serialize feature, so that it works as expected.

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Migration Guide

The bevy_remote feature of bevy now enables the serialize feature automatically. If you wish to use bevy_remote without enabling the serialize feature for Bevy subcrates, you must import bevy_remote on its own.

[mweatherley]

I'm not sure if there is some protocol about whether this should be done at the level of bevy or bevy_internal, but either is fine with me :)