Support managing development dependencies (?)

[rdw-software]

From what I can tell (going by the source), lit doesn't appear to support something akin to npm's devDependencies field.

I would love to have a way of installing development tools, like my own testing framework, and allow developers to automatically install them with lit, but not as part of the regular dependencies that are deployed to end users. This would be equivalent to npm install --save-dev, where development dependencies are managed normally but separately from the regular ones.

The only way I can think of possibly achieving that would be adding them as regular dependencies, and then excluding the files. This should in theory lead to them not being added when using lit make, but it seems like a hack and there's probably cases where it won't work as expected if it was never designed for this purpose.

Is there a "proper" way of accomplishing this? If there isn't, is this a feature that would be useful and worth adding?