Worked around Unity 2019's invalid DLL broken errors

Unity 2019 refused to load the iOS Resolver DLL as it has a reference
to a potentially missing DLL in the public interface even though
the public method would not be called unless the iOS platform is selected
and therefore the DLL reference would be resolved successfully.

Bug: 136566524
Fixes #247

Change-Id: I0869dfa0b3d03e6a7ea8bd2636d3f46e7dafb67b

Author: Stewart Miles

CHANGELOG.md

@@ -1,3 +1,10 @@
+# Version 1.2.122 - Jul 2, 2019
+## Bug Fixes
+* iOS Resolver: Worked around Unity not loading the iOS Resolver DLL as it
+  referenced the Xcode extension in a public interface.  The iOS Resolver
+  DLL still references the Xcode extension internally and just handles
+  missing type exceptions dynamically.
+
 # Version 1.2.121 - Jun 27, 2019
 ## Bug Fixes
 * Android Resolver: Fixed warning about missing Packages folder when loading

source/IOSResolver/src/IOSResolver.cs

@@ -1579,10 +1579,10 @@ public static IEnumerable<string> XcodeTargetNames {
     /// <summary>
     /// Get Xcode target GUIDs using a method that works across all Unity versions.
     /// </summary>
-    /// <param name="project">Project to query.</param>
+    /// <param name="xcodeProject">UnityEditor.iOS.Xcode.PBXProject project to query.</param>
     /// <returns>List of target GUIDs.</returns>
-    public static IEnumerable<string> GetXcodeTargetGuids(
-            UnityEditor.iOS.Xcode.PBXProject project) {
+    public static IEnumerable<string> GetXcodeTargetGuids(object xcodeProject) {
+        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