[Core feature request] Allow passing non-string outputs to inputs

[krzema12]

What feature do you need?
If an action returns e. g. an integer as its output, I'd like to be able to pass it as input to another action in a type-safe manner.

Do you have an example usage?
Best if a YAML snippet is pasted here, or if your project is open-source, an URL to your workflow.
TODO

[Vampire]

Maybe something like this until denotable union types are supported and then unifying the fields: Vampire@87efab0