Configure repository.directory for monorepo packages

[jasonkarns]

Summary

Configure each package's package.json#repository.directory
property to properly reflect the location of the package within
the repository.

This is the standard configuration value for deep-linking into a
package's directory within a monorepo.

npm RFC: https://github.com/npm/rfcs/blob/latest/implemented/0010-monorepo-subdirectory-declaration.md

This will ensure the packages' pages on npmjs.org will link to the
correct directory.

Also, eventually, it will ensure the npm repo command opens to the
correct location: npm/cli#163

Lastly, this is required for monorepo packages to be successfully
published to the GitHub Package Registry (if that is ever considered in
the future).
https://help.github.com/en/packages/using-github-packages-with-your-projects-ecosystem/configuring-npm-for-use-with-github-packages#publishing-multiple-packages-to-the-same-repository

Test plan

n/a

Issues

[mjc1283]

Very cool, I didn't know this was being standardized!

[jasonkarns]

@mjc1283 same! I only learned about it when I tried to publish our fork to github package registry. Since the package registry ties packages to a repo, having multiple packages published to a single repo is problematic. So they require this configuration to make it work (somehow). All the rest I only stumbled on afterwards!

(And it's a bummer that the npm CLI is still pending the PR to respect it. I use the npm repo command heavily and it's annoying that it doesn't yet work well with monorepos. 😞 )