Feature request: serde Serialize and Deserialize support for repr_c::String and repr_c::Vec

[mtorromeo]

Hi,
firstly, thanks for the great library, which is already a huge help in simplifying my ffi code!

I would like to request a feature that would let me avoid having to duplicate a lot of struct definitions.

What I have is a bunch of structs containing Strings and Vecs and deriving Serialize and Deserialize, which I also want to use in the ffi interface and right now I have to duplicate them changing every String and Vec with their repr_c counterpart and implementing a From impl to convert them. For example:

#[derive(Serialize, Deserialize)]
struct ExampleData {
  name: String,
  list: Vec<String>,
}

mod ffi {
  #[derive_ReprC]
  #[repr(C)]
  struct ExampleData {
    name: repr_c::String,
    list: repr_c::Vec<repr_c::String>,
  }

  impl From<super::ExampleData> for ExampleData {
    fn from(value: super::TestData) -> Self {
      Self {
        name: value.name.into(),
        list: repr_c::Vec::from(value.list.into_iter().map(Into::<repr_c::String>::into).collect::<Vec<repr_c::String>>()),
      }
    }
  }
}

It would be great if I could simply do this instead:

#[derive_ReprC]
#[repr(C)]
#[derive(Serialize, Deserialize)]
struct ExampleData {
  name: repr_c::String,
  list: repr_c::Vec<repr_c::String>,
}

But this is not possible right now since repr_c::String and repr_c::Vec do not implement Serialize and Deserialize.