Add migration instructions for isToolshown rename

MIGRATION.md

@@ -2,6 +2,7 @@
 
 - [From version 6.4.x to 6.5.0](#from-version-64x-to-650)
   - [React18 new root API](#react18-new-root-api)
+  - [Renamed isToolshown to showToolbar](#renamed-istoolshown-to-showtoolbar)
   - [Deprecated register.js](#deprecated-registerjs)
   - [Dropped support for addon-actions addDecorators](#dropped-support-for-addon-actions-adddecorators)
   - [Vite builder renamed](#vite-builder-renamed)
@@ -213,6 +214,21 @@ module.exports = {
 };
 ```
 
+### Renamed isToolshown to showToolbar
+
+Storybook's [manager API](docs/addons/addons-api.md) has deprecated the `isToolshown` option (to show/hide the toolbar) and renamed it to `showToolbar` for consistency with other similar UI options.
+
+Example:
+
+```js
+// .storybook/manager.js
+import { addons } from '@storybook/addons';
+
+addons.setConfig({
+  showToolbar: false,
+});
+```
+
 ### Deprecated register.js
 
 In ancient versions of Storybook, addons were registered by referring to `addon-name/register.js`. This is going away in SB7.0. Instead you should just add `addon-name` to the `addons` array in `.storybook/main.js`.

docs/snippets/common/storybook-config-layout.js.mdx

@@ -18,11 +18,11 @@ addons.setConfig({
     collapsedRoots: ['other'],
   },
   toolbar: {
-    title: { hidden: false, },
-    zoom: { hidden: false, },
-    eject: { hidden: false, },
-    copy: { hidden: false, },
-    fullscreen: { hidden: false, },
+    title: { hidden: false },
+    zoom: { hidden: false },
+    eject: { hidden: false },
+    copy: { hidden: false },
+    fullscreen: { hidden: false },
   },
 });
-```
+```

lib/api/src/modules/layout.ts

@@ -3,6 +3,8 @@ import pick from 'lodash/pick';
 import deepEqual from 'fast-deep-equal';
 import { themes } from '@storybook/theming';
 import type { ThemeVars } from '@storybook/theming';
+import { once } from '@storybook/client-logger';
+import dedent from 'ts-dedent';
 
 import merge from '../lib/merge';
 import type { State, ModuleFn } from '../index';
@@ -25,7 +27,10 @@ export interface Layout {
   showNav: boolean;
   showTabs: boolean;
   showToolbar: boolean;
-  isToolshown?: boolean; // deprecated
+  /**
+   * @deprecated
+   */
+  isToolshown?: boolean;
 }
 
 export interface UI {
@@ -222,6 +227,11 @@ export const init: ModuleFn = ({ store, provider, singleStory }) => {
       const { theme, selectedPanel, ...options } = provider.getConfig();
 
       if (options?.layout?.isToolshown !== undefined) {
+        once.warn(dedent`
+          The "isToolshown" option is deprecated. Please use "showToolbar" instead.
+
+          See https://github.com/storybookjs/storybook/blob/next/MIGRATION.md#renamed-istoolshown-to-showtoolbar
+        `);
         options.layout.showToolbar = options.layout.isToolshown;
       }