Add readonly to function types in typing_print json

Add readonly to function types in typing_print json

Summary:
Implement some extra readonly info into json for typing_print. This allows `--type-at-pos-batch` to read readonlyness of parameters, return types, and readonly_this.

This field only appears when a function has the readonly property, so backwards compatibility is preserved.

Specifically,
a function type will contain the following optional JSON fields:

```
{
"kind": "function",
"readonly_this": true # if the function is readonly
"params": ...
"readonly_return":true # if the function returns a readonly result
"result": ...
}
```
Parameters will have a readonly field:
```
{
callConvention: ...
readonly: true # if parameter is readonly
type: ...
}
```

Reviewed By: viratyosin

Differential Revision: D36384909

fbshipit-source-id: b2ef532991737e6ad25856907d517756fa285541