run svelte-kit sync in all workspace directories

[Rich-Harris]

Closes #6617. In the case where @sveltejs/kit is installed to an npm workspace root, we run svelte-kit sync in all the directories specified in pkg.workspaces, taking account of things like ./packages/*. (Though I've just read https://docs.npmjs.com/cli/v7/configuring-npm/package-json#workspaces and it seems that more complex globbing patterns are allowed, so this probably needs to use a globbing library.)

Difficult to add tests for this, so I didn't.

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[dummdidumm]

Looks good, but I have one related improvement suggestion

[dominikg]

What about other monorepo/workspace solutions (pnpm, yarn, lerna?). Do they have similar issues? At least pnpm uses a different way to declare workspace packages

Does sync validate that it is called on a package using svelte-kit? If not the current implementation in this PR could lead to problems in a workspace that mix kit and other svelte projects.

[Rich-Harris]

What about other monorepo/workspace solutions (pnpm, yarn, lerna?). Do they have similar issues?

AFAIK — certainly for pnpm — the package will be 'installed' in each workspace directory that uses it. npm is different in that packages are only installed at the workspace root, hence the need to check for a pkg.workspaces

Does sync validate that it is called on a package using svelte-kit?

It does not. Definitely an edge case but I can add a check for that