Add Textual Encoding codec

[XAMPPRocky]

Rasn should be capable of outputting what the ASN.1 textual encoding of a type. I think this is something that would be useful for writing modules and for debugging types. I think this should probably be able to work with just the AsnType trait, since we don't actually need to traverse the type through the codec traits.

Example

#[derive(AsnType)]
struct Foo {
  member: String
}

println!("{}", rasn::text::to_string::<Foo>());

Output

Foo  ::=  SEQUENCE  {
     member       UTF8String
}

[Nicceboy]

Would it make sense to make Debug implementation to produce that presentation, and to_string just wraps it? Or is there some use case where debug could give more information and this presentation would hide the details.

[XAMPPRocky]

I don't think it should be debug, because Debug semantically means rust's debug representation. Where as I would want to guarantee that we're generating semantically.

I think that would make sense as the display representation of the AST we generate.

[Nicceboy]

Yeah, Display would make much more sense. To clarify, we are talking about value notation? I think I could try to implement this in close future if no one else does not want.

[XAMPPRocky]

Oh no, I guess we're talking about two separate kinds text notation. I was focusing on the type notation, so you can literally print your type as a valid ASN.1 module. I think we should also support value notation.

[Nicceboy]

Ah, so we are using Rust to generate valid ASN.1 Schema 😄 I guess it makes now much more sense to keep in AsnType. Maybe Display should be reserved for value notation.