Support packageJson.preRelease: true along packageJson.version

[hediet]

Conceptually, the pre-release flag is tied to the version number.
However, at the moment, the version is specified in package.json, but the pre-release flag is passed in as cli argument, both for package and publish.
This also makes me wonder what happens when a vsix is packaged with --pre-release, but published without (and vice versa, packaged without and published with).
If the pre-release flag was read from package.json (from source or inside the given vsix file), it would be quite clear.

To fix issues like #947 and make it less confusing, I'd suggest that by default, the pre-release flag is read from a package.json property 'preRelease'.

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It seems like publish only uses the --pre-release flag if the vsix still needs to be build (i.e. if no vsix is specified).

[lppedd]

Coincidentally, I've wrapped vsce in an Nx plugin, where I read a custom preRelease: boolean property, which is then passed to the tool as command line parameter.

This looks good!

[benibenj]

Thanks for the suggestion! I think setting the --pre-release flag via CLI is actually preferable, especially for CI pipelines where packaging and publishing can be done separately for release and pre-release builds. Relying on a package.json property would require modifying the file between steps, which adds unnecessary complexity and risk. Since the --pre-release flag is only used during publish when a VSIX needs to be built, there's little room for confusion, its behavior should be straightforward.

To make sure there is not any confusion, we could also throw an error if the user passes CLI flags (like --pre-release) that are only applicable during packaging when attempting to publish an already packaged extension.