remove serde_derive

[jakobhellermann]

alternative to #384

Cuts the critical compilation chain of bevy further from syn -> serde_derive -> glam -> bevy_math -> bevy_reflect to syn -> bevy_reflect_derive -> bevy_reflect which is a few seconds faster.

but it makes the code less maintainable (especially if you plan to add more types with a serde derives so I can understand if you don't want to merge this. I just copied the output of rust-analyzer's Expand macro recursively and cleaned it up a bit.

[bitshifter]

Seems like this doesn't work with no_std.

[bitshifter]

Since this was the only type using derive I'm OK with providing an implementation by hand.

It should move to src/features/impl_serde.rs with the rest of them though.

It might warrant adding a test to that file as well.

[bitshifter]

Looks good but this should move to src/features/impl_serde.rs.

[bitshifter]

Thanks!