add support for building examples

[databasedav]

rebased version of #457

resolves #423

[ctron]

Thanks for the PR! Sorry not taking a look at this earlier. I'll give it a manual try and check.

[ctron]

Ok, I tried to use this in a way like:

trunk serve --example vanilla

However, it won't work. As our examples also have a configuration and have the index.html in the examples folder.

I am wondering what the use case of that PR in its current form would be?

[databasedav]

However, it won't work. As our examples also have a configuration and have the index.html in the examples folder.

I am wondering what the use case of that PR in its current form would be?

the PR is quite minimal and doesn't introduce any special considerations for how examples are organized, e.g. like the examples in this repo are, with separate Cargo.tomls for each example, instead it just maintains the status quo and expects the index.html to exist in the directory where trunk is run, this lets one run trunk ... for examples compatible with the classic cargo run --example ...

for example, i released a vendored version of trunk here https://github.com/databasedav/trunk/releases/tag/v0.0.1, which i use in my ci here https://github.com/databasedav/haalka/blob/dd675822a9441f343be64cd280b8c69cb92fc44c/.github/workflows/build_and_deploy_example.yaml#L29 to run a just command here (one for webgl2, one for webgpu) https://github.com/databasedav/haalka/blob/dd675822a9441f343be64cd280b8c69cb92fc44c/.github/workflows/build_and_deploy_example.yaml#L34-L39, which generates an index.html for the example in the root of the checked out directory and then calls trunk build ... here https://github.com/databasedav/haalka/blob/dd675822a9441f343be64cd280b8c69cb92fc44c/justfile#L46-L48

the generated files are viewable (for example) here https://github.com/databasedav/haalka/tree/0b77b1686637ea77659e8a7f61c2ede34e75d263/examples/webgl2/counter and served via github pages here https://databasedav.github.io/haalka/examples/webgl2/counter/

i think having trunk serve --example vanilla work out of the box would be nice, but would be too prescriptive for how consumers should organize their examples e.g. requiring subfolders per example with the corresponding index.html in the subfolder, instead this PR just lets consumers at the very least build examples with the native cargo ... --example ... and manage the configuration with status quo trunk semantics