docs: enable sourcemaps in examples

[rrrnld]

This enables source maps in all example builds, as discussed in https://github.com/thi-ng/umbrella/discussions/483.

I think the patch was applied correctly, but I wasn't able to test all examples. From what I can tell there are two different configs:

// taken from examples/mandelbrot, but is also in examples/shader-ast-workers and others
export default {
    build: { target: "esnext" },
    worker: { format: "es" },
};

and the simpler one without a worker config:

// used almost everywhere
export default {
    build: { target: "esnext" },
};

I have bult the pointfree-geom and mandelbrot examples and tested them via yarn build && yarn preview and both work fine!

[postspectacular]

🎉 Thank you so much, @heyarne! I think those 2 examples you listed are the only ones with workers, but I will also update this config in the scripts/make-example script so that all future examples also inherit that setting...