Serde tagging

[oscartbeaumont]

Right now specta_typescript always applies Serde tagging.

We investigated moving this process to specta_serde but that's not possible because Typescript is tagged by content while other languages are not. So you end up with something like:

Say you have enum T { A }. A is exported to TS as null by default but when you run it through specta_serde what does it become? You would think it goes from Fields::Unit to Fields::Unnamed(vec![ Field::new(DataType::Literal(LiteralType::String("A") ]). Now that's fine but then export that same typemap to Rust and you effectively get enum T { A("A") } which is not possible.

Should we make it configurable?

untagged in the equivalent of the approach we looked at for `specta_serde

Should we move tagging configuration to specta_typescript specific context? Well the Rust exporter should include the json tagging attribute so maybe this is just not possible, idk.

[oscartbeaumont]

EnumRepr should probs be Option<EnumRepr> so specta_serde can adjust the default.