Add a new param to GetXcodeTargetGuids()

Add a new param to GetXcodeTargetGuids() to return guids from all
targets in Unity 2019.3+.

By default, GetXcodeTargetGuids() only returns guids of the target which
includes Unity and third-party libraries. It is `Unity-iPhone` for Unity
2019.2 or below or `UnityFramework` for Unity 2019.3+.

Introduce a new param "includeAllTargets" to return guids of all
targets, excluding test targets, when multiple Xcode project target is
supported from Unity 2019.3+.

This is useful when we need to add target membership to all targets for
special cases.  For example, adding `Google-Services.plist` to all
targets in order to support the case when the user's project has
dependency on Swift framework, such as Facebook SDK.

Bug: 174515725

Change-Id: I2374800cefc21d79cf9a7fb6f66a39f0acbbdade

Author: chkuang-g

source/IOSResolver/src/IOSResolver.cs

@@ -1683,15 +1683,34 @@ public static IEnumerable<string> XcodeTargetNames {
     /// <param name="xcodeProject">UnityEditor.iOS.Xcode.PBXProject project to query.</param>
     /// <returns>List of target GUIDs.</returns>
     public static IEnumerable<string> GetXcodeTargetGuids(object xcodeProject) {
+        return GetXcodeTargetGuids(xcodeProject, includeAllTargets: false);
+    }
+
+    /// <summary>
+    /// Get Xcode target GUIDs using a method that works across all Unity versions.
+    /// </summary>
+    /// <param name="xcodeProject">UnityEditor.iOS.Xcode.PBXProject project to query.</param>
+    /// <param name="includeAllTargets">If true, if multiple xcode project targets is supported, ex.
+    /// Unity 2019.3+, returns both guids of 'UnityFramework' and the main target 'Unity-iPhone`.
+    /// Otherwise, only return the guid of the target which contains Unity libraries. For Unity
+    /// 2019.2 or below, it is the guid of `Unity-iPhone`; for Unity 2019.3+, it is the guid of
+    /// `UnityFramework`.
+    /// </param>
+    /// <returns>List of target GUIDs.</returns>
+    public static IEnumerable<string> GetXcodeTargetGuids(object xcodeProject,
+                                                          bool includeAllTargets) {
         var project = (UnityEditor.iOS.Xcode.PBXProject)xcodeProject;
         var targets = new List<string>();
         if (MultipleXcodeTargetsSupported) {
             // In Unity 2019.3+ TargetGuidByName will throw an exception if the Unity-iPhone target
             // is requested so we need to use instance methods to fetch the GUIDs of each target.
             // NOTE: The test target is not exposed.
             try {
-                foreach (var guidMethod in
-                         new[] { "GetUnityFrameworkTargetGuid" }) {
+                var guidMethods = new List<string>() {"GetUnityFrameworkTargetGuid"};
+                if (includeAllTargets) {
+                    guidMethods.Add("GetUnityMainTargetGuid");
+                }
+                 foreach (var guidMethod in guidMethods) {
                     targets.Add((string)VersionHandler.InvokeInstanceMethod(project, guidMethod,
                                                                             null));
                 }