fix: set correct linking location for yarn_install using package.json from external repository

[gregmagolan]

Fixes #3323

Verified on repro repository, https://github.com/mhevery/repro-bazel-nested-project

gregs-mbp:repro-bazel-nested-project greg$ bazel build @child//packages/core
INFO: Analyzed target @child//packages/core:core (12 packages loaded, 99 targets configured).
INFO: Found 1 target...
Target @child//packages/core:core up-to-date:
  bazel-bin/external/child/packages/core/main.js
INFO: Elapsed time: 0.447s, Critical Path: 0.01s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action

gregs-mbp:repro-bazel-nested-project greg$ cd child
gregs-mbp:child greg$ bazel build //packages/core
INFO: Analyzed target //packages/core:core (10 packages loaded, 94 targets configured).
INFO: Found 1 target...
Target //packages/core:core up-to-date:
  bazel-bin/packages/core/main.js
INFO: Elapsed time: 2.755s, Critical Path: 0.01s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action

[thesayyn]

That's ridiculously simple.