Support web manifest v3 for web extensions in @parcel/config-webextension

[burhanuday]

🙋 feature request

Currently, "manifest_version": 3, in manifest.json results in error

🚨 Build failed.

@parcel/transformer-webextension: Invalid Web Extension manifest

  manifest.json:5:23
    4 |   "version": "0.1.2",
  > 5 |   "manifest_version": 3,
  >   |                       ^ Possible values: "2"
    6 |   "background": {
    7 |     "service_worker": "src/js/inject.js"

🤔 Expected Behavior

Build succesfully without errors

😯 Current Behavior

Results in above error

💁 Possible Solution

🔦 Context

 "@parcel/config-webextension": "^2.0.0",
 "parcel": "^2.0.0"

💻 Examples

[burhanuday]

PR here - #7050
close issue when PR gets merged

[mischnic]

Duplicate of #6079