Windows icons not set

# Bug Report

## Problem

### What is expected to happen?

The appx (Windows Store) package should have my app icon set as its icon.

If what's below isn't the correct way to configure this for Electron, the correct solution should ideally be documented.

### What does actually happen?

My configuration below and icons are ignored; the default Electron icons are used instead.

```

```

## Information

You can unzip the appx file and see that only the default Electron icons appear under assets.

### Command or Code

`cordova build electron`

### Environment, Platform, Device

macOS 10.14.6

### Version information

Cordova 9.0.0

## Checklist

- [X] I searched for existing GitHub issues
- [X] I updated all Cordova tooling to most recent version
- [X] I included all the necessary information above

Start by reproducing the issue with `cordova build electron` and inspecting the generated appx package's assets. Trace how the listed icon configuration is handled during Electron packaging; done means the configured Windows icon files appear in the appx instead of the default Electron icons, or the supported configuration is documented.

Written by the indexing model from the issue text.