Preserve user's pods when building incrementally.

Attempt to preserve user's pods when building Xcode incrementally if
multiple Xcode project is supported.

Currently it only preserve the pods added into the target
which contains Unity libraries.  That is, `Unity-iPhone` for Unity
2019.2 or below and `UnityFramework` for Unity 2019.3+.

Change-Id: I46a4838a9e61cda14f6be2bb67716d6474eed1b8

source/IOSResolver/src/IOSResolver.cs

@@ -831,6 +831,18 @@ public static string XcodeUnityFrameworkTargetName {
         }
     }
 
+    /// <summary>
+    /// Name of the Xcode target which contains Unity libraries.
+    /// From Unity 2019.3+, Unity includes all its libraries and native libraries under Assets
+    /// folder to 'UnityFramework' instead of 'Unity-iPhone'.
+    /// </summary>
+    public static string XcodeTargetWithUnityLibraries {
+        get {
+            return MultipleXcodeTargetsSupported ?
+                    XcodeUnityFrameworkTargetName : XcodeMainTargetName;
+        }
+    }
+
     /// <summary>
     /// Initialize the TARGET_NAME property.
     /// This will be "Unity-iPhone" in versions of Unity (2019.3+) that added support for using
@@ -1975,7 +1987,8 @@ private static void ParseUnityDeps(string unityPodfilePath) {
                 continue;
             }
             // TODO: Properly support multiple targets.
-            if (line.StartsWith(String.Format("target '{0}' do", XcodeMainTargetName))) {
+            if (line.StartsWith(String.Format("target '{0}' do",
+                    XcodeTargetWithUnityLibraries))) {
                 capturingPodsDepth++;
                 continue;
             }