RestHalf spec for single param

[trydofor]

POST with single parameter is recommended to post data directly, eg. common types in server,

• Boolean:boolean - true
• BigDecimal/Long/Integer:number/string - 123 / "123"
• String:string - "string"
• LocalDateTime:string - "2021-06-06 06:06:06"
• LogLevel.TRACE:string - "TRACE"

eg. common types in client,

• JSON.stringify("string") - "string"
• JSON.stringify(123) - 123
• JSON.stringify(true) - true
• JSON.stringify({str:"string",dec:123,bol:true}) - {"str":"string","dec":123,"bol":true}

alibaba/fastjson2#1537