dillon1000/react

[rust] Improve estree serialization

Updates to use our own codegen'd `Serialize` implementation for AST node types. 
Notably, this allows us to ensure that we always emit a `type` field, even when 
the type is obvious from context (serde doesn't do this) and avoid 
double-emitting `type` fields (which serde can do if you try to force a tag to 
be emitted). We still use the Deserialize impl because it works fine for our 
purposes.