Fix typing parse fn with NODE_STREAM_INPUT arg (#30251)

As stated in the Papaparse documentation
(https://github.com/mholt/PapaParse#papa-parse-for-node), calling Papa.parse
with NODE_STREAM_INPUT argument returns a Duplex that is both readable and
writable. This is for the use case of piping a ReadableStream through Papa CSV
parsing and continuing the stream chain.

types/papaparse/index.d.ts

@@ -7,6 +7,7 @@
 //                 Alberto Restifo <https://github.com/albertorestifo>
 //                 Behind The Math <https://github.com/BehindTheMath>
 //                 3af <https://github.com/3af>
+//                 Janne Liuhtonen <https://github.com/jliuhtonen>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.2
 
@@ -23,7 +24,7 @@ export function parse(file: File, config?: ParseConfig): ParseResult;
 
 export function parse(stream: NodeJS.ReadableStream, config?: ParseConfig): ParseResult;
 
-export function parse(stream: typeof NODE_STREAM_INPUT, config?: ParseConfig): NodeJS.ReadableStream;
+export function parse(stream: typeof NODE_STREAM_INPUT, config?: ParseConfig): NodeJS.ReadWriteStream;
 
 /**
  * Unparses javascript data objects and returns a csv string

types/papaparse/papaparse-tests.ts

@@ -9,6 +9,7 @@ import {
 	ParseMeta,
 	ParseResult
 } from "papaparse";
+import { Readable } from "stream";
 
 /**
  * Parsing
@@ -40,8 +41,19 @@ Papa.parse(file, {
 	}
 });
 
+const readable = new Readable()
+const rows = [
+	"1,2,3",
+	"4,5,6"
+]
 
-Papa.parse(Papa.NODE_STREAM_INPUT);
+rows.forEach(r => {
+	readable.push(r);
+});
+
+const papaStream: NodeJS.ReadWriteStream = Papa.parse(Papa.NODE_STREAM_INPUT);
+
+readable.pipe(papaStream);
 
 /**
  * Unparsing