Add command to get information about single package

[swissspidy]

As suggested in wp-cli/i18n-command#53 (comment), there could be a new wp package version command to get the version of a single command.

Perhaps this could also just be wp package get <package> [--fields=<fields>] so one can easily get any specific field for a package.

Ideally we abstract the code in such a way that a single package is able to get its own version using that way.

[schlessera]

That is non-trivial. Inside of the code, the versions don't exist. We can only fetch and store them during the Composer build phase, which means adding something like https://github.com/Ocramius/PackageVersions

[schlessera]

Once we force Composer v2+ as a dependency here, we can move forward with this, as the above mentioned PackageVersions package is now a direct part of Composer from v2 onwards.

[gilzow]

Once we force Composer v2+ as a dependency here

@schlessera any ETA on when this will be able to happen?

[schlessera]

@gilzow Right now we allow for both v1 and v2 of Composer to be used, and the built Phar already defaults to v2.
It might be feasible to phase out v1 with WP-CLI v3, but we'll have to see at that point what the installation numbers are.