feat: recursively merge package.json scripts field from build configuration

[kuhe]

Issue #, if available:
closes #1125

Description of changes:

One of the build options for code generation is:

packageJson | required=No | Custom package.json properties that will be merged with the base package.json. The default value is an empty object.

Because of shallow merging, it is difficult for example to merge script entries like

{
  "scripts": {
    "build": "<from codegen>",
    "test": "<user provided>"
  }
}

This PR changes the behavior to recursive merging for only the scripts field. I do not expect anyone to be relying on the existing shallow merge behavior, because every code generated field in "scripts" is there for a reason.

More specific customization of the package.json object can be done after the build, if needed.

Recursive merging is not done for other fields, to avoid mixing user and generated nested fields in e.g. authorship metadata or bundler instruction metadata.

[kstich]

Is the merge on line 57 not sufficient for this?

[kuhe]

It's a shallow merge, so this does the following:

Default:

{
  "name": "A",
  "scripts": {
    "build": "..."  
  },
  "metadata": "A"
}

User supplied:

{
  "name": "B",
  "scripts": {
    "test": "..."  
  }
}

• create the merged pkg.scripts object.

{
  "build": "...",
  "test": "..."
}

• do the normal shallow merge

{
  "name": "B",
  "scripts": {
    "test": "..."  
  },
  "metadata": "A"
}

• write the merged pkg.scripts onto the shallow merge

{
  "name": "B",
  "scripts": {
    "build": "...",
    "test": "..."  
  },
  "metadata": "A"
}

[kuhe]

Need to address CI failures, I think they're related to this PR and not the intermittent kind