Add FileSystemSynchronized objects

[hyzyla]

I've added new classes PBXFileSystemSynchronizedRootGroup and PBXFileSystemSynchronizedBuildFileExceptionSet that were introduced in Xcode 16.

I used an example pbxproj from this project Score-Tally (MIT) in tests but struggled with naming because "XCConfigurationList" is serialized without a space for some reason. Should I just remove the space in test file and move on, or is this issue somehow related to my pull request?

    -           3E7D825F2C3892C4006B36EB /* Build configuration list for PBXProject "Score Tally" */ = {
    +           3E7D825F2C3892C4006B36EB /* Build configuration list for PBXProject "ScoreTally" */ = {

https://github.com/EvanBacon/xcode/issues/17