[BUG]: _favicon/* is removed from web_accessible_resources

[vitalets]

🐛 bug report

Per extensions docs I can define _favicon/* in web_accessible_resources to make favicons accessible on the webpages.
Currently Parcel removes _favicon/* from web_accessible_resources and favicons can't be displayed.

🎛 Configuration (.babelrc, package.json, cli command)

manifest.json:

  "web_accessible_resources": [
    {
      "resources": ["_favicon/*"],
      "matches": ["<all_urls>"]
    }
  ]

command:

parcel build manifest.json --config @parcel/config-webextension

🤔 Expected Behavior

The output manifest contains _favicon/* entry:

  "web_accessible_resources": [
    {
      "resources": ["_favicon/*"],
      "matches": ["<all_urls>"]
    }
  ]

😯 Current Behavior

The output manifest has resources as empty array:

  "web_accessible_resources": [
    {
      "resources": [],
      "matches": ["<all_urls>"]
    }
  ]

💁 Possible Solution

Provide custom transformer for manifest.json and manually add _favicon/* to web_accessible_resources.

🔦 Context

💻 Code Sample

🌍 Your Environment

"parcel": "^2.14.4",