bevy_reflect: implement Reflect for SmolStr

[Vrixyz]

Objective

To upgrade winit's dependency, it's useful to reuse SmolStr, which replaces/improves the too restrictive Key letter enums.

As Input is a resource it should implement Reflect through all its fields.

Solution

Add smol_str to bevy_reflect supported types, behind a feature flag.

This PR blocks winit's upgrade PR: #8745.

Current state

• I'm discovering bevy_reflect, I appreciate all feedbacks, and send me your nitpicks!
• Lacking more tests

[MrGVSV]

Looking good! Just a few comments.

[alice-i-cecile]

This is a good idea, and the use of a feature flag is wise. Generally looks good, although I agree with the nits raised :)

[Vrixyz]

This is a good idea, and the use of a feature flag is wise. Generally looks good, although I agree with the nits raised :)

I thought too, but as current implementation of #8745, I changed the exposed character key to contain a SmolStr, effectively adding a dependency to the bevy_input.

So I aggregated the features within bevy rather than fragmenting too much the features: 012bd90. (Now that I think about it, maybe we shouldn't add this into the bevy feature just yet, but include it in the winit PR?)

We could also add more granular features but I think that's not the goal of this PR.

I'm setting this out of draft mode.

[MrGVSV]

Now that I think about it, maybe we shouldn't add this into the bevy feature just yet, but include it in the winit PR?

Yeah the changes are small enough that you probably could. Approving this PR anyways in case it makes more sense to merge beforehand.

We could also add more granular features but I think that's not the goal of this PR.

Yeah I think it would be good to have a feature for any bevy-crate dependency (i.e. a bevy_math feature to add glam, etc.). But yeah we can focus on that another time.

[alice-i-cecile]

This is useful in its own right, and much easier to review like this than as part of the mega upgrade PR. Merging now.