Add support for WorkspaceSettings

[pepicrft]

Resolves #358

Short description 📝

Workspaces contain a WorkspaceSettings.xcsettings file which contains settings such as a the build system that Xcode should use. xcodeproj does not have support for that file (yet).

Solution 📦

Add support for parsing and writing WorkspaceSettings.xcsettings files.

Implementation 👩‍💻👨‍💻

• Add WorkspaceSettings model.
• Change buildSystem to be of type BuildSystem instead of String?
• Add a method to write the file back to disk.
• Add a workspaceSettings attribute to the XCSharedData model.

Note: There are some extra changes as a result of running swiftformat for the project. Those changes have nothing to do with bringing the feature onto the project.

[pepicrft]

I plan to define a new type and use it instead of String?:

enum BuildSystem {
  case original
  case new
}

[yonaskolb]

Awesome! 👏
Perhaps master could have swift format applied? It would make the changes here easier to see

[johndpope]

cool cool - thanks