feat: add type of toc

packages/react/src/mdx.d.ts

@@ -0,0 +1,7 @@
+declare module '*.mdx' {
+  import type { MDXProps } from 'mdx/types'
+  import type { Toc } from '@stefanprobst/rehype-extract-toc'
+
+  export const tableOfContents: Toc
+  export default function MDXContent(props: MDXProps): JSX.Element
+}