docs: support multiple sidebars in a project (#11768)

* changed to new sidebar across projects except resources

* finalize multi sidebar support

* clean up

* remove redundant property

* small changes

* fixes

* generate

* fix error

* fix initial open

www/packages/build-scripts/src/utils/validate-sidebar-unique-ids.ts

@@ -0,0 +1,22 @@
+import { Sidebar } from "types"
+
+export const validateSidebarUniqueIds = (
+  sidebars: (Sidebar.RawSidebar | Sidebar.SidebarItemSidebar)[],
+  sidebarIds = new Set<string>()
+): void => {
+  for (const sidebar of sidebars) {
+    if (sidebarIds.has(sidebar.sidebar_id)) {
+      throw new Error(`Duplicate sidebar item id found: ${sidebar.sidebar_id}`)
+    }
+
+    sidebarIds.add(sidebar.sidebar_id)
+
+    const children = (
+      "items" in sidebar ? sidebar.items : sidebar.children || []
+    ).filter(
+      (child) => child.type === "sidebar"
+    ) as Sidebar.SidebarItemSidebar[]
+
+    validateSidebarUniqueIds(children, sidebarIds)
+  }
+}