fix(link): scope npm link <path> --workspace to the workspace, not the root

[manzoorwanijk]

In continuation of our exploration of using install-strategy=linked in the Gutenberg monorepo, which powers the WordPress Block Editor.

npm link <path> --workspace=<ws> did not scope the operation to the target workspace.
The linked dependency was attached to the root project instead, and with --save (or --save-dev/--save-optional/etc.) the file: spec was written to the root package.json rather than <ws>/package.json.
npm install <path> --workspace=<ws> --save behaved correctly, so only npm link was affected.

The cause is in Link.linkInstall() in lib/commands/link.js, which built the local Arborist without the workspaces option and passed workspaces only to reify().
Arborist decides which node receives the add request from this.options.workspaces, which is captured at construction time, not from the reify-time option.
buildIdealTree merges reify options into a local variable and #parseSettings never copies options.workspaces into this.options, so the reify-time value never reached #applyUserRequests.
With this.options.workspaces left empty, the add and the save were applied to the root node.

The fix passes workspaces: this.workspaceNames to the local Arborist constructor, matching how lib/commands/install.js already does it.
Physical placement is unchanged: under the default hoisted strategy the symlink still hoists to the root node_modules, identical to npm install --workspace.

References

Fixes #9590
Related #9589

[github-actions]

🎉 Backport to release/v11 created: #9595