[LG-5285] feat(split-button): export MenuItem and MenuItemProps (#3331)

* chore(split-button): export MenuItem and MenuItemProps

* docs(split-button): README

* chore(split-button): changeset

Author: stephl3

.changeset/new-points-relate.md

@@ -0,0 +1,5 @@
+---
+'@leafygreen-ui/split-button': minor
+---
+
+[LG-5285](https://jira.mongodb.org/browse/LG-5285): pass through and export `MenuItem` and `MenuItemProps` to fix cross-dependency issues with `@leafygreen-ui/menu`

packages/split-button/README.md

@@ -27,22 +27,20 @@ npm install @leafygreen-ui/split-button
 ## Example
 
 ```js
-
-import { SplitButton } from `@leafygreen-ui/split-button`;
-import { MenuItem } from '@leafygreen-ui/menu';
+import { MenuItem, SplitButton } from '@leafygreen-ui/split-button';
 
 <SplitButton
   label="label"
-  menuItems={
-    [
-      <MenuItem key='0'>Menu Item</MenuItem>,
-      <MenuItem key='1' disabled>Disabled Menu Item</MenuItem>,
-      <MenuItem key='2' description="I am also a description">
-        Menu Item With Description
-      </MenuItem>
-    ]
-  }
-/>
+  menuItems={[
+    <MenuItem key="0">Menu Item</MenuItem>,
+    <MenuItem key="1" disabled>
+      Disabled Menu Item
+    </MenuItem>,
+    <MenuItem key="2" description="I am also a description">
+      Menu Item With Description
+    </MenuItem>,
+  ]}
+/>;
 ```
 
 ## Properties

packages/split-button/src/index.ts

@@ -8,3 +8,4 @@ export {
   Variant,
 } from './SplitButton';
 export { DEFAULT_LGID_ROOT, getLgIds, type GetLgIdsReturnType } from './utils';
+export { MenuItem, type MenuItemProps } from '@leafygreen-ui/menu';