Add favicon48 prop to iconPaths option to define a favicon to show in Google search result

[StaymanHou]

What problem does this feature solve?

Currently the plugin only generates favicon16 and favicon32 tags when compiled. That works fine for browsers but doesn't comply with the Google search appearance guidelines for defining a favicon. - https://support.google.com/webmasters/answer/9290858?hl=en

The guidelines specify that a valid favicon must be a multiple of 48px square. Please provide a option to generate a 48x48 favicon tag.

What does the proposed API look like?

pwa.iconPaths

{
  favicon48: 'img/icons/favicon-48x48.png',
  favicon32: 'img/icons/favicon-32x32.png',
  favicon16: 'img/icons/favicon-16x16.png',
  appleTouchIcon: 'img/icons/apple-touch-icon-152x152.png',
  maskIcon: 'img/icons/safari-pinned-tab.svg',
  msTileImage: 'img/icons/msapplication-icon-144x144.png'
}

And generate <link rel=icon type=image/png sizes=48x48 href=img/icons/favicon-48x48.png>

[LinusBorg]

@sodatea this seems like a good idea. Agree? Then I'll do a PR

[haoqunjiang]

Looks good 🙂