Replace Prefire with a very similar but simpler and more direct approach (#3232)

* Replace Prefire with a very similar but simpler and more direct approach

* Move PreviewTest snapshots to their new location (snapshotting default, mirrors UITests)

* Update acknowledgements

* Switch snapshot configuration extensions to a custom version

* Exclude snapshots from the PreviewTests target

* Fix acknowledgements

* Rename snapshotting preference keys

* Remove `skipPackagePluginValidation`

ElementX/Sources/Screens/RoomDetailsScreen/View/RoomDetailsScreen.swift

@@ -392,12 +392,12 @@ struct RoomDetailsScreen_Previews: PreviewProvider, TestablePreview {
     static var previews: some View {
         RoomDetailsScreen(context: simpleRoomViewModel.context)
             .previewDisplayName("Simple Room")
-            .snapshot(delay: 2)
+            .snapshotPreferences(delay: 2)
         RoomDetailsScreen(context: dmRoomViewModel.context)
             .previewDisplayName("DM Room")
-            .snapshot(delay: 0.25)
+            .snapshotPreferences(delay: 0.25)
         RoomDetailsScreen(context: genericRoomViewModel.context)
             .previewDisplayName("Generic Room")
-            .snapshot(delay: 0.25)
+            .snapshotPreferences(delay: 0.25)
     }
 }