breaking(types): type arrays as read-only (#1335)

Closes #1259

* breaking(types): type arrays as read-only

* Run "yarn build:docs"

* test: assert read-only arrays

src/ContextMenu/ContextMenu.svelte

@@ -6,7 +6,7 @@
   /**
    * Specify an element or list of elements to trigger the context menu.
    * If no element is specified, the context menu applies to the entire window
-   * @type {null | HTMLElement | HTMLElement[]}
+   * @type {null | ReadonlyArray<null | HTMLElement>}
    */
   export let target = null;
 

src/ContextMenu/ContextMenuGroup.svelte

@@ -1,5 +1,5 @@
 <script>
-  /** @type {string[]} */
+  /** @type {ReadonlyArray<string>} */
   export let selectedIds = [];
 
   /** Specify the label text */