Add a `pnpm store path` command to print the location of the pnpm store
as the CLI would resolve it. This allows the user to inspect the current
store location, as well as allows external tooling (like shell scripts)
to locate the pnpm store without needing to make assumptions about its
location or needing to load the `@pnpm/store-path` module.
This command differs from running `pnpm get store`, as `pnpm get store`
prints "undefined" in the case that no custom store path has been set,
which requires external tooling to have knowledge about where pnpm
locates its store in the default case.
close#2575
