Add submitter parameter to FormData constructor (#9145)

Summary:
This has been widely available for a [while](https://caniuse.com/?search=FormData.submitter) now

References:
- https://xhr.spec.whatwg.org/#interface-formdata
- https://developer.mozilla.org/en-US/docs/Web/API/FormData/FormData
- whatwg/xhr#366 (review) (discussion on why null is allowed)

Pull Request resolved: #9145

Reviewed By: SamChou19815

Differential Revision: D57181660

fbshipit-source-id: 98502daf0a26d361820739a90607e7a2d1275d66

lib/bom.js

@@ -626,7 +626,7 @@ declare class DOMParser {
 type FormDataEntryValue = string | File
 
 declare class FormData {
-    constructor(form?: HTMLFormElement): void;
+    constructor(form?: HTMLFormElement, submitter?: HTMLElement | null): void;
 
     has(name: string): boolean;
     get(name: string): ?FormDataEntryValue;

tests/bom/FormData.js

@@ -5,6 +5,9 @@ const a: FormData = new FormData(); // correct
 new FormData(''); // incorrect
 new FormData(document.createElement('input')); // incorrect
 new FormData(document.createElement('form')); // correct
+new FormData(document.createElement('form'), null); // correct
+new FormData(document.createElement('form'), document.createElement("button")); // correct
+new FormData(document.createElement('form'), "submitter"); // incorrect
 
 // has
 const b: boolean = a.has('foo'); // correct