[v2][source-contentful] Restore legacy sizes and resolutions fragments (#5678)
[v2][source-contentful] Restore legacy sizes and resolutions fragments (#5678)

* [v2] Restore legacy sizes and resolutions fragments

* Reword TODO a little bit

gatsbyjs/gatsby,gatsbyjs/gatsby,fk/gatsby,fk/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,mingaldrichgan/gatsby,0x80/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,0x80/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,mingaldrichgan/gatsby,fk/gatsby,mingaldrichgan/gatsby