Allow "main" field in template.js to populate destination template's package.json #8373

Is your proposal related to a problem?

In order to have a template work with electron, the "main" field in the resulting template must be something like "main": "build/electron.js". Currently, there is no way to allow this, as a "main" field in template.json will not populate into the template.

Describe the solution you'd like

"main": "build/electron.js" in template.json transpiles to "main": "build/electron.js" in package.json at root of template.