fix(nuxt): Create declaration files for Nuxt module (#13909)

[Nuxt module builder](https://github.com/nuxt/module-builder) uses the
closest `tsconfig.json` and this had `"declaration": false`. I added
another `tsconfig.json` closer to the module to generate those
declarations.

fixes #13899

packages/nuxt/src/tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "extends": "../tsconfig.json",
+
+  "compilerOptions": {
+    // nuxt-module-build uses the closest `tsconfig.json` to build the Nuxt module declarations
+    "declaration": true,
+  }
+}