`ts(optional)` should be working on any which has `skip_serializing_if`

[xiao-e-yun]

Describe the bug ts(optional) can't support skip_serializing_if attr

To Reproduce

1. Write this code

   #[ts(export)]
   #[derive(TS , Serialize)]
   pub struct A{
   #[ts(optional)]
   #[serde(skip_serializing_if = "<[_]>::is_empty")]
   pub arrays: Vec<String>,
   }

2. Throw error: optional can only be used on an Option type

Expected behavior return type

export type A = { arrays?: Array<string>, };

[NyxCode]

On 8.1.0, you can use

    #[ts(as = "Option<Vec<String>>", optional)]
    my_vec: Vec<String>

On the latest master (and soon in 9.0.0), you can then do

    #[ts(as = "Option<_>", optional)]
    my_vec: Vec<String>

It is by design that the TS types we generate match the type in Rust. This has been discussed at length before, see #175.