Updated index.d.ts to match text-encoding npm module (#29404)

types/text-encoding/index.d.ts

@@ -2,6 +2,7 @@
 // Project: https://github.com/inexorabletash/text-encoding
 // Definitions by: MIZUNE Pine <https://github.com/pine613>
 //                 Mohsen Azimi <https://github.com/mohsen1>
+//                  Thomas Nicollet <https://github.com/nwmqpa>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.8
 
@@ -31,11 +32,20 @@ interface TextEncodeOptions {
     stream?: boolean;
 }
 
+interface TextDecoderOptions {
+    stream?: boolean;
+}
+
 interface TextEncoder {
     readonly encoding: string;
     encode(input?: string, options?: TextEncodeOptions): Uint8Array;
 }
 
+interface TextDecoder {
+    readonly encoding: string;
+    decode(input?: Uint8Array, options?: TextDecoderOptions): string;
+}
+
 declare module "text-encoding" {
     export = TextEncoding;
 }