[Doc] Fix old MUI import path in code snippets

docs/BoxStackGrid.md

@@ -17,7 +17,7 @@ It accepts all [the `sx` prop](./SX.md), which makes it easy to style:
 
 {% raw %}
 ```jsx
-import { Box } from '@material-ui/core';
+import { Box } from '@mui/material';
 
 const MyComponent = () => (
     <Box
@@ -104,7 +104,7 @@ To learn more, read the [Material-UI Box documentation](https://mui.com/material
 ![Stack](./img/stack.webp)
 
 ```jsx
-import { Stack } from '@material-ui/core';
+import { Stack } from '@mui/material';
 
 const Items = () => (
     <Stack spacing={2}>
@@ -154,7 +154,7 @@ Use the `divider` prop to insert an element between each child.
 
 {% raw %}
 ```jsx
-import { Stack } from '@material-ui/core';
+import { Stack } from '@mui/material';
 
 export const DividerStack = () => (
     <div>

docs/FilterLiveSearch.md

@@ -23,7 +23,7 @@ To add a full-text search filter on customers, include `<FilterLiveSearch>` in a
 {% raw %}
 ```tsx
 import { List, FilterLiveSearch } from 'react-admin';
-import { Card, CardContent } from '@material-ui/core';
+import { Card, CardContent } from '@mui/material';
 import { LastVisitedFilter, HasOrderedFilter, HasNewsletterFilter, SegmentFilter } from './filters';
 
 const FilterSidebar = () => (

docs/useLockOnCall.md

@@ -23,7 +23,7 @@ Use this hook in a toolbar, to let the user lock the record manually.
 ```jsx
 import { Edit, SimpleForm, TextInput } from 'react-admin';
 import { useLockOnMount } from '@react-admin/ra-realtime';
-import { Alert, AlertTitle, Box, Button } from '@material-ui/core';
+import { Alert, AlertTitle, Box, Button } from '@mui/material';
 
 const PostAside = () => {
     const [doLock, { data, error, isLoading }] = useLockOnCall();

docs/useLockOnMount.md

@@ -23,7 +23,7 @@ Use this hook e.g. in an `<Edit>` component to lock the record so that it only a
 ```jsx
 import { Edit, SimpleForm, TextInput } from 'react-admin';
 import { useLockOnMount } from '@react-admin/ra-realtime';
-import { Alert, AlertTitle, Box } from '@material-ui/core';
+import { Alert, AlertTitle, Box } from '@mui/material';
 
 const PostAside = () => {
     const { isLocked, error, isLoading } = useLockOnMount();