Add description to generated packages

[ayys]

Description

Current state: package.json (for javascript projects) and pyptoject.toml (for python projects)
don't have a description field. This PR adds the field to those files.

Note: I added a function get_description_from_webc_manifest to wasmer-pack/pirita.rs. This is very
similar to the get_package_name_from_manifest function in webc crate, and should probably belong there. If so, I need guidance moving it there.

Context

While trying to publish a python package generated by wasmer-pack to pypi, I ran into an error from
twine.

ERROR    `long_description` has syntax errors in markup and would not be rendered on PyPI.
         No content rendered from RST source.
WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.
Checking dist/polyvalid-0.1.4.tar.gz: PASSED with warnings
WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.
WARNING  `long_description` missing.

This was solved when I added the description and readme fields to my pyproject.toml. This PR itself doesn't solve my problem - I still need the readme field added to pyproject.toml.

Checklist

• Is this a user-facing change? If so, update CHANGELOG.md

Fixes #6.

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[ayys]

Not needed anymore. Will remove this.

[Michael-F-Bryan]

Thanks for making this PR @ayys!

I've suggested a slightly different way to get the description. It means we'll need to also modify the code generating pyproject.toml, but should theoretically be cleaner because we avoid error cases and only do python-specific requirements in the wasmer_pack::py module.

[Michael-F-Bryan]

This should be safe to remove now.

[Michael-F-Bryan]

This function is probably better written as the following one-liner:

use webc::metadata::annotations::Wapm;

m.package_annotation("wapm")
    .ok()
    .map(|Wapm { description, .. }| description)

(which can be inlined into `metadata()` if you want)

fn metadata(webc: &WebC<'_>, fully_qualified_package_name: &str) -> Result<Metadata, Error> {
    let (unversioned_name, version) = fully_qualified_package_name.split_once('@').unwrap();
    let package_name = unversioned_name
        .parse()
        .context("Unable to parse the package name")?;

    let mut metadata = Metadata::new(package_name, version);

    if let Ok(Wapm { description, .. }) = webc.manifest.package_annotation("wapm") {
        metadata = metadata.with_description(description);
     }

    Ok(metadata)
}

That way we don't crash when the "wapm" annotation is missing, and we return Option<String> rather than using an empty string.

I feel like if PyPI requires a description to be provided, we should generate an error at the top of wasmer_pack::py::generate_python() or fall back to the empty string by making this description field required and doing description.as_deref().unwrap_or_default() here.

What are your thoughts?