Convert to folder references where possible

[aokj4ck]

Description

• Xcode 16 introduced Folder references which 1:1 match the filesystem with Swift sources
  • indicated with a blue folder icon instead of the previous gray folder icon
• (All Swift Packages only use Folder references.)
• Previously, Group references could match the filesystem but often would have:
  • unused sources that were missed from deletion during refactoring
  • symlinks or mis-organized source files
  • merge conflicts with pbxproj!
• By using "Convert to Folder" on most groups we avoid all these problems.
• This will dramatically reduce the risk of merge conflicts in Mastodon.pbxproj.

Discussion: https://mjtsai.com/blog/2024/10/07/xcode-16-folders-and-groups/
Documentation: https://developer.apple.com/documentation/xcode/managing-files-and-folders-in-your-xcode-project#Convert-groups-to-folders

Downsides

• Sources are listed alphabetically and cannot be re-ordered
• Not sure if this is compatible with Swiftgen or Sourcery!

Not Included

• Sourcery templates
• Resources with localizations that were not 1:1 with the filesystem

Documentation

There are several benefits to using folders instead of groups when organizing your Xcode project files. Folders have a much smaller representation in the project file, which can result in fewer merge conflicts because when you add or remove files to the project you don’t modify the project file. Additionally, your Xcode project file automatically updates as you make changes to the file system.

To convert a group into a folder using the Convert to Folder option within the Project navigator:

1. Select one or more groups in your Project navigator.

2. Control-click the selected group(s) and select Convert to Folder.

Xcode checks to see if the groups in your Xcode project match the underlying files and directories on disk. If they do, Xcode converts each group into a folder. If the groups and underlying directory structures don’t match, Xcode displays a dialog with a Show Details button. Click the Show Details button to see a list of the files and directories Xcode couldn’t convert.

To convert the files Xcode displays in Show Details, make the file and directory structure in Xcode match what Finder displays on disk. Either modify the file and group structure in Xcode to match the file and directory structure in Finder, or modify the file and directory structure in Finder to match the contents of your groups in Xcode. Then select the groups, Control-click, and choose Convert to Folder again.

— https://developer.apple.com/documentation/xcode/managing-files-and-folders-in-your-xcode-project#Convert-groups-to-folders

[aokj4ck]

PR-1499 will achieve some of the changes from #1238 and prevent the conditions that left unused source files