Add the ability to apply decorators to anonymous struct enum variants

[ahou8]

Consider the following enum decorated with the swift protocol Equatable.

#[typeshare(swift = "Equatable")]
#[serde(tag = "type", content = "content")]
enum MyEnum {
    MyVariant {
        a: String,
        b: f64
    }
}

Running this through typeshare, the following is generated

/// Generated type representing the anonymous struct variant `MyVariant` of the `MyEnum` Rust enum
public struct MyEnumMyVariantInner: Codable {
	public let a: String
	public let b: Double

	public init(a: String, b: Double) {
		self.a = a
		self.b = b
	}
}
public enum MyEnum: Codable, Equatable {
	case myVariant(MyEnumMyVariantInner)
       
        ...
}

Although Equatable was applied to MyEnum, it was not applied to MyEnumMyVariantInner. And there doesn't seem to be any way to do so.

My first thought was to apply #[typeshare(swift = "Equatable")] on the enum variant, but that was ignored.

#[typeshare(swift = "Equatable")]
#[serde(tag = "type", content = "content")]
enum MyEnum {
+  #[typeshare(swift = "Equatable")]
    MyVariant {
        a: String,
        b: f64
    }
}