fix: create links relative to the target

Added link deps need to be relative to the package they're being added
to, not the project root.  In the past the project root was the only
place you could add things but workspaces changed this.

Author: wraithgar

workspaces/arborist/lib/arborist/build-ideal-tree.js

@@ -514,7 +514,9 @@ Try using the package name instead, e.g:
   // This returns a promise because we might not have the name yet,
   // and need to call pacote.manifest to find the name.
   async [_add] (tree, { add, saveType = null, saveBundle = false }) {
-    const path = this.idealTree.target.path
+    // If we have a link it will need to be added relative to the target's path
+    const path = tree.target.path
+
     // get the name for each of the specs in the list.
     // ie, doing `foo@bar` we just return foo
     // but if it's a url or git, we don't know the name until we