fix tabs + localStorage

Summary:
Key fix is
```diff
-    'Tabs:' + localStorageKeyOverride ?? keys.join(','),
+    'Tabs:' + (localStorageKeyOverride ?? keys.join(',')),
```

Previously it worked like `('Tabs:' + localStorageKeyOverride) ?? keys.join(','),` which always evaluated to `"Tabs:undefined"`. This means that all tabs that were not using localStorageKeyOverride were reusing the same localstorage key. If you open some tabs with A, B, and C tabs. And open tab B. Then open other tabs with D, E, and F. No tab would be selected as the default value would be B.

The second part it extracing keys from `items` prop instead of children.

Reviewed By: lblasa

Differential Revision: D50411422

fbshipit-source-id: 30f70c4347649f29e8c8ff1f2f38fdca7e826198

desktop/flipper-plugin/src/ui/Tabs.tsx

@@ -25,7 +25,7 @@ export function Tabs({
   localStorageKeyOverride, //set this if you need to have a dynamic number of tabs, you do *not* need to namespace with the plugin name
   ...baseProps
 }: {grow?: boolean; localStorageKeyOverride?: string} & TabsProps) {
-  const keys: string[] = [];
+  const keys: string[] = baseProps.items?.map((item) => item.key) ?? [];
   const keyedChildren = Children.map(children, (child: any, idx) => {
     if (!child || typeof child !== 'object') {
       return;
@@ -53,7 +53,7 @@ export function Tabs({
   });
 
   const [activeTab, setActiveTab] = useLocalStorageState<string | undefined>(
-    'Tabs:' + localStorageKeyOverride ?? keys.join(','),
+    'Tabs:' + (localStorageKeyOverride ?? keys.join(',')),
     undefined,
   );