Modify Xcode project after build in Unity

PostBuild.cs

#if UNITY_EDITOR

using System;
using System.IO;
using UnityEngine;
using UnityEditor;
using UnityEditor.Callbacks;
using UnityEditor.iOS.XcodeNew;

public class PostBuild {

    [PostProcessBuildAttribute]
    public static void OnPostprocessBuild(BuildTarget target, string pathToBuiltProject) {
#if UNITY_IOS
        var projectPath = PBXProject.GetPBXProjectPath(pathToBuiltProject);
        var project = new PBXProject();
        project.ReadFromFile(projectPath);

        var infoPlist = new PlistDocument();
        var infoPlistPath = pathToBuiltProject + "/Info.plist";
        infoPlist.ReadFromFile(infoPlistPath);

        AddFrameworks(project);
        CopyPodfile(pathToBuiltProject);
        ConfigureFabric(infoPlist, project);

        infoPlist.WriteToFile(infoPlistPath);
        project.WriteToFile(projectPath);
#endif
    }

    private static string GetDefaultTarget(PBXProject project) {
        return project.TargetGuidByName(PBXProject.GetUnityTargetName());
    }

    private static void AddFrameworks(PBXProject project) {
        Debug.Log("Adding frameworks");

        var defaultTarget = GetDefaultTarget(project);
        project.AddFrameworkToProject(defaultTarget, "AdSupport.framework", false);
    }

    private static void CopyPodfile(string pathToBuiltProject) {
        var podfilePath = "Assets/BoxLoader/iOS/Podfile";
        var destPodfilePath = pathToBuiltProject + "/Podfile";

        Debug.Log(String.Format("Copying Podfile from {0} to {1}", podfilePath, destPodfilePath));

        if (!File.Exists(destPodfilePath)) {
            FileUtil.CopyFileOrDirectory(podfilePath, destPodfilePath);
        } else {
            Debug.Log("Podfile already exists");
        }
    }

    private static void ConfigureFabric(PlistDocument infoPlist, PBXProject project) {
        Debug.Log("Adding Fabric info to Info.plist");

        const string FabricApiKey = "<YOUR API KEY>";
        const string FabricSecret = "<YOUR SECRET>";

        var fabricDict = new PlistElementDict();
        fabricDict.SetString("APIKey", FabricApiKey);

        var fabricKitsArray = fabricDict.CreateArray("Kits");
        var crashlyticsKit = fabricKitsArray.AddDict();
        crashlyticsKit.SetString("KitName", "Crashlytics");
        crashlyticsKit.CreateDict("KitInfo");

        infoPlist.root["Fabric"] = fabricDict;

        Debug.Log("Adding a run script phase for Fabric");

        var defaultTarget = GetDefaultTarget(project);
        var fabricScript = project.ShellScriptByName(defaultTarget, "Fabric");

        if (fabricScript == null) {
            fabricScript = String.Format("\"${{PODS_ROOT}}/Fabric/run\" {0} {1}", FabricApiKey, FabricSecret);
            project.AppendShellScriptBuildPhase(defaultTarget, "Fabric", "", fabricScript);
        }
    }
}

#endif

Where does project.ShellScriptByName and AppendShellScriptBuildPhase come from? I dont see that in the current docs https://docs.unity3d.com/ScriptReference/iOS.Xcode.PBXProject.html

I can found the API here:
https://bitbucket.org/Unity-Technologies/xcodeapi/src/fbd0cb184b437b751ac0e2213779c310aaba0952/Xcode/PBXProject.cs?at=stable&fileviewer=file-view-default

However, it is internal API, how can I make it public? Thanks!!