Workaround to link Swift Standard Libraries

The Xcode project generate from Unity may not be able to link Swift
Standard Libaries properly if
1. Some pods include Swift frameworks
2. Podfile sets to link frameworks statically

The workround attempts to fix this by
1. Add a Dummy.swift file to the Xcode project.
2. Enable `CLANG_ENABLE_MODULES` and `ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES`
   build settings.
3. Change `SWIFT_VERSION` to the value specified in iOS Resolver
   settings. Default to "5".

This workaround is turned OFF by default.

source/IOSResolver/src/IOSResolver.cs

@@ -1048,7 +1048,7 @@ public static bool PodfileStaticLinkFrameworks {
     }
 
     /// <summary>
-    /// Ehether to enable Swift Framework support workaround.
+    /// Whether to enable Swift Framework support workaround.
     /// If enabled, iOS Resolver adds a Dummy.swift to the generated Xcode project, and change build
     //  properties in order to properly include Swift Standard Libraries.
     /// </summary>
@@ -2030,7 +2030,6 @@ internal static void AddDummySwiftFile(
     public static void OnPostProcessGenPodfile(BuildTarget buildTarget,
                                                string pathToBuiltProject) {
         if (!InjectDependencies() || !PodfileGenerationEnabled) return;
-        Log("OnPostProcessGenPodfile!", level: LogLevel.Error);
         GenPodfile(buildTarget, pathToBuiltProject);
     }
 

source/IOSResolver/src/IOSResolverSettingsDialog.cs

@@ -284,8 +284,8 @@ public void OnGUI() {
                     settings.swiftLanguageVersion =
                         EditorGUILayout.TextField(settings.swiftLanguageVersion);
                     GUILayout.EndHorizontal();
-                    GUILayout.Label("Used to set 'SWIFT_VERSION' build setting in Xcode. Leave " +
-                                    "it blank to update it manually.");
+                    GUILayout.Label("Used to override 'SWIFT_VERSION' build setting in Xcode. " +
+                                    "Leave it blank to prevent override.");
                 }
             }