Add react webpack example

[Mivr]

Related to aspect-build/bazel-examples#276 and aspect-build/bazel-examples#83

This PR adds a react JS Webpack example using SWC for transpilation and Webpack for bundling.

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[alexeagle]

Looks great, thank you!

FYI I've been working the last couple days to change the existing react example to stop using react-scripts, but I'll switch it to vite/vitest so it will still be nicely orthogonal to this one.