node plugin: record the yarn.lock file

[come-maiz]

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• If this is a bugfix. Have you checked that there is a bug report open for the issue you are trying to fix on bug reports?
• If this is a new feature. Have you discussed the design on the forum?
• Have you successfully run ./runtests.sh static?
• Have you successfully run ./runtests.sh unit?

---

This is part of #1453.
Requires #1523

[kalikiana]

The fact that the test can get away with arbitrary data makes me think the plugin should at least do basic validation - but then it took all of 5 minutes in DuckDuckGo to find that it's not YAML but some 500 lines of custom parsing...

So, I think some validation would be nice, whether that's a regex or nodejs command, before saving the lock contents in the manifest. And using a real-looking example in the test. But I'll leave this as a would-be-nice suggestion.

[come-maiz]

If the plugin can build the package with the contents of the yarn.lock, we should record whatever was used despite of the specific value. If the value is not valid, the plugin should fail before recording anything.

[sergiusens]

tested, works as expected