refactor(examples): switch examples from cra to nextjs

examples/nextjs/pages/MultiFlows/index.tsx

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+import React, { FC } from 'react';
+
+import ReactFlow, {
+  addEdge,
+  Background,
+  Node,
+  Edge,
+  Connection,
+  ReactFlowProvider,
+  useNodesState,
+  useEdgesState,
+  MarkerType,
+} from '@react-flow/core';
+
+import styles from './multiflows.module.css';
+
+const initialNodes: Node[] = [
+  {
+    id: '1',
+    type: 'input',
+    data: { label: 'Node 1' },
+    position: { x: 250, y: 5 },
+    className: 'light',
+  },
+  {
+    id: '2',
+    data: { label: 'Node 2' },
+    position: { x: 100, y: 100 },
+    className: 'light',
+  },
+  {
+    id: '3',
+    data: { label: 'Node 3' },
+    position: { x: 400, y: 100 },
+    className: 'light',
+  },
+  {
+    id: '4',
+    data: { label: 'Node 4' },
+    position: { x: 400, y: 200 },
+    className: 'light',
+  },
+];
+
+const initialEdges: Edge[] = [
+  {
+    id: 'e1-2',
+    source: '1',
+    target: '2',
+    animated: true,
+    markerEnd: { type: MarkerType.Arrow },
+  },
+  { id: 'e1-3', source: '1', target: '3' },
+];
+
+const Flow: FC<{ id: string }> = ({ id }) => {
+  const [nodes, , onNodesChange] = useNodesState(initialNodes);
+  const [edges, setEdges, onEdgesChange] = useEdgesState(initialEdges);
+
+  const onConnect = (params: Edge | Connection) =>
+    setEdges((eds) => addEdge(params, eds));
+
+  return (
+    <ReactFlowProvider>
+      <ReactFlow
+        nodes={nodes}
+        edges={edges}
+        onNodesChange={onNodesChange}
+        onEdgesChange={onEdgesChange}
+        onConnect={onConnect}
+        id={id}
+      >
+        <Background />
+      </ReactFlow>
+    </ReactFlowProvider>
+  );
+};
+
+const MultiFlows: FC = () => (
+  <div className={styles.multiflows}>
+    <Flow id='flow-a' />
+    <Flow id='flow-b' />
+  </div>
+);
+
+export default MultiFlows;

examples/nextjs/pages/MultiFlows/multiflows.module.css

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+.multiflows {
+  display: flex;
+  height: 100%;
+}
+
+.multiflows :global .react-flow {
+  width: 100%;
+  height: 100%;
+}
+
+.multiflows :global .react-flow:first-child {
+  border-right: 2px solid #333;
+}