fix: add sourceMaps: true to vite-plugin-babel config examples

[whdjh]

Fixes #8215

The vite-plugin-babel configuration examples were missing sourceMaps: true in babelConfig, causing broken sourcemaps when debugging React Compiler-optimized components.

Updated both the Vite alternative setup and React Router sections to include the missing option.

Summary

Adds sourceMaps: true to the babelConfig in both the Vite
alternative setup and React Router installation examples.

Problem

When using vite-plugin-babel with React Compiler, the current
docs omit sourceMaps: true from the Babel configuration. This
causes sourcemaps to include React Compiler-optimized code paths
instead of the original source, making debugging significantly
harder.

Reproduction: https://github.com/andrew-locklair-fs/react-vite-compiler-repro

Fix

Added sourceMaps: true to babelConfig in:

1. Vite section — alternative vite-plugin-babel example
2. React Router section — vite-plugin-babel example

Fixes #8215

[meta-cla]

Hi @whdjh!

Thank you for your pull request and welcome to our community.

Action Required

In order to merge any pull request (code, docs, etc.), we require contributors to sign our Contributor License Agreement, and we don't seem to have one on file for you.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at cla@meta.com. Thanks!

[github-actions]

Size changes

Details

📦 Next.js Bundle Analysis for react-dev

This analysis was generated by the Next.js Bundle Analysis action. 🤖

This PR introduced no changes to the JavaScript bundle! 🙌

[meta-cla]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Meta Open Source project. Thanks!