Add File system synchronized groups comparator

[kwridan]

Resolves: #140

Describe your changes

• Adding a new comparator to diff the Xcode 16 synchronized groups which can include sources

Testing performed

Run xcdiff on the new fixture and verify it flags diffs for the mismatching groups

swift run xcdiff -p1 Fixtures/xcode16_syncgroups_1/Project.xcodeproj -p2 Fixtures/xcode16_syncgroups_2/Project.xcodeproj -v

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.02%. Comparing base (c48fb45) to head (8636f33).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #143      +/-   ##
==========================================
- Coverage   97.05%   97.02%   -0.03%     
==========================================
  Files          52       53       +1     
  Lines        2986     3024      +38     
==========================================
+ Hits         2898     2934      +36     
- Misses         88       90       +2     

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[kwridan]

An alternative name of the comparator could be buildable_folders which seems to be the name used in some of the Xcode docs

https://developer.apple.com/documentation/updates/xcode#Projects-and-workspaces

Minimize project file changes and avoid conflicts with buildable folder references. Convert an existing group to a buildable folder with the Convert to Folder context menu item in the Project Navigator. Buildable folders only record the folder path into the project file without enumerating the contained files, minimizing diffs to the project when your team adds or removes files, and avoiding source control conflicts. To use a folder as an opaque copiable resource, the default behavior before Xcode 16, uncheck the Build Folder Contents option in the File Inspector.

[marciniwanicki]

Looks good, thank you @kwridan 👍