feat: Add `closedby` to `HTMLDialogAttributes` (dialog element) (#15458)

* Adding the `closedby` attribute to dialog element

Spec: https://html.spec.whatwg.org/#attr-dialog-closedby

* Adding changeset

* Update .changeset/metal-spoons-scream.md

---------

Co-authored-by: Rich Harris <hello@rich-harris.dev>

.changeset/metal-spoons-scream.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: Add `closedby` property to HTMLDialogAttributes type

packages/svelte/elements.d.ts

@@ -957,6 +957,7 @@ export interface HTMLDelAttributes extends HTMLAttributes<HTMLModElement> {
 
 export interface HTMLDialogAttributes extends HTMLAttributes<HTMLDialogElement> {
 	open?: boolean | undefined | null;
+	closedby?: 'any' | 'closerequest' | 'none' | undefined | null;
 }
 
 export interface HTMLEmbedAttributes extends HTMLAttributes<HTMLEmbedElement> {