(fix) add FormDataEvent (#1760)

#1755

Author: dummdidumm

packages/svelte2tsx/svelte-html-do-not-use.d.ts

@@ -87,7 +87,7 @@ export interface DOMAttributes<T extends EventTarget> {
 	'on:reset'?: FormEventHandler<T> | undefined | null;
 	'on:submit'?: EventHandler<Event, T> | undefined | null; // TODO make this SubmitEvent once we require TS>=4.4
 	'on:invalid'?: EventHandler<Event, T> | undefined | null;
-
+	'on:formdata'?: EventHandler<Event & { readonly formData: FormData; }, T> | undefined | null; // TODO make this FormDataEvent once we require TS>=4.4
 
 	// Image Events
 	'on:load'?: EventHandler | undefined | null;

packages/svelte2tsx/svelte-jsx.d.ts

@@ -348,6 +348,7 @@ declare namespace svelte.JSX {
       onsubmit?: EventHandler<SubmitEvent, T> | undefined | null;
       oninvalid?: EventHandler<Event, T> | undefined | null;
       onbeforeinput?: EventHandler<InputEvent, T> | undefined | null;
+      'on:formdata'?: EventHandler<FormDataEvent, T> | undefined | null;
 
       // Image Events
       onload?: EventHandler | undefined | null;