Unify linear interpolation traits

[Architector4]

In Bevy, there are two traits with methods for linear interpolation:

• bevy_aniumation::animatable::Animatable
• bevy_math::common_traints::StableInterpolate

The former has an interpolate method, and the latter has interpolate_stable method, with the same signature. They also have different requirements (former wants Reflect and also fn blend implementation, latter needs it to be stable interpolation).

It might be a good idea to have a single general "interpolatable" trait, either unifying all of these properties into one, or as a supertrait of both.

(I apologize for using the non-fancy blank issue template; none of the others felt like they fit, since this isn't really a feature request nor a bug with Bevy)

[greeble-dev]

There's one in progress PR that would satisfy this: #18674.

[Architector4]

OH, that's absolutely beautiful. Sorry, I checked in the issues but not in the pull requests for anything existing. Considering that that PR is about exactly what this issue is, feel free to close this as you see fit to avoid double tracking lol

[greeble-dev]

That's fine, I'll leave this issue open as I don't know if that PR will land.