feat: msix auto-updater

[bitdisaster]

Description of Change

This PR implements MSIX auto-updating according to electron/rfcs#21 . The new upater module supports auto-updating via:

• Mac.Squirrel JSON server format

{
  "url": "https://mycompany.example.com/myapp/package.msix",
  "name": "My Release Name",
  "notes": "Theses are some release notes innit",
  "pub_date": "2013-09-18T12:29:53+01:00"
}

• Mac.Squirrel static update file format

{
  "currentRelease": "2.0.0",
  "releases": [
    {
      "version": "1.0.0",
      "updateTo": {
        "version": "1.0.0",
        "pub_date": "2013-09-18T12:29:53+01:00",
        "notes": "Theses are some release notes innit",
        "name": "1.2.1",
        "url": "https://mycompany.example.com/myapp/package_1.msix""
      }
    },
    {
      "version": 2.0.0",
      "updateTo": {
        "version": "2.0.0",
        "pub_date": "2014-09-18T12:29:53+01:00",
        "notes": "Theses are some more release notes innit",
        "name": "1.2.3",
        "url": "https://mycompany.example.com/myapp/package_2.msix"
      }
    }
  ]
}

• direct MSIX url link
  https://mycompany.example.com/myapp/package.msix

Additonally, MSIX supports downgrading by setting allowAnyVersion. False by default.

 autoUpdater.setFeedURL({ url: 'https://mycompany.example.com/myapp/package.msix', allowAnyVersion: true }

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant API documentation, tutorials, and examples are updated and follow the documentation style guide
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: