chore: enable MDX type checking (#6368)

global.ts

···
+import type { mdxComponents } from '@/next.mdx.use.mjs';
+
+declare global {
+  type MDXProvidedComponents = typeof mdxComponents;
+}

next.mdx.use.mjs

···
 /**
  * A full list of React Components that we want to pass through to MDX
  *
- * @type {import('mdx/types').MDXComponents}
+ * @satisfies {import('mdx/types').MDXComponents}
  */
 export const mdxComponents = {
   // Legacy Component

tsconfig.json

···
     "plugins": [{ "name": "next" }],
     "baseUrl": "."
   },
+  "mdx": {
+    "checkMdx": true
+  },
   "include": [
     "next-env.d.ts",
+    "**/*.mdx",
     "**/*.ts",
     "**/*.tsx",
     ".next/types/**/*.ts",