Parser: allow 'options' to explicitly accept undefined (#3678)
Parser: allow 'options' to explicitly accept undefined (#3678)

Continuation of #3670
Basically allow to have code like this:
```js
parse(document, GraphQLServerConfig.parserOptions)
```
to pass TS check with 'exactOptionalPropertyTypes'
graphql/graphql-js,graphql/graphql-js,graphql/graphql-js