Fix broken UnityReady trigger in iOS exports. (#747)

* Fix UnityReady trigger being placed on the wrong line in UnityAppController.mm

* Fix a compilation error in Unity 2020.3 and 2021.1.

Author: timbotimbo

example/unity/DemoApp/Assets/FlutterUnityIntegration/Editor/Build.cs

@@ -211,7 +211,7 @@ private static void DoBuildAndroid(String buildPath, bool isPlugin, bool isRelea
             #if UNITY_2022_1_OR_NEWER
                 PlayerSettings.SetIl2CppCompilerConfiguration(BuildTargetGroup.Android, isReleaseBuild ? Il2CppCompilerConfiguration.Release : Il2CppCompilerConfiguration.Debug);
                 PlayerSettings.SetIl2CppCodeGeneration(UnityEditor.Build.NamedBuildTarget.Android, UnityEditor.Build.Il2CppCodeGeneration.OptimizeSize);
-            #elif UNITY_2020_3_OR_NEWER
+            #elif UNITY_2021_2_OR_NEWER
                 PlayerSettings.SetIl2CppCompilerConfiguration(BuildTargetGroup.Android, isReleaseBuild ? Il2CppCompilerConfiguration.Release : Il2CppCompilerConfiguration.Debug);
                 EditorUserBuildSettings.il2CppCodeGeneration = UnityEditor.Build.Il2CppCodeGeneration.OptimizeSize;
             #endif
@@ -371,7 +371,7 @@ private static void BuildIOS(String path, bool isReleaseBuild)
             #if UNITY_2022_1_OR_NEWER
                 PlayerSettings.SetIl2CppCompilerConfiguration(BuildTargetGroup.iOS, isReleaseBuild ? Il2CppCompilerConfiguration.Release : Il2CppCompilerConfiguration.Debug);
                 PlayerSettings.SetIl2CppCodeGeneration(UnityEditor.Build.NamedBuildTarget.iOS, UnityEditor.Build.Il2CppCodeGeneration.OptimizeSize);
-            #elif UNITY_2020_3_OR_NEWER
+            #elif UNITY_2021_2_OR_NEWER
                 PlayerSettings.SetIl2CppCompilerConfiguration(BuildTargetGroup.iOS, isReleaseBuild ? Il2CppCompilerConfiguration.Release : Il2CppCompilerConfiguration.Debug);
                 EditorUserBuildSettings.il2CppCodeGeneration = UnityEditor.Build.Il2CppCodeGeneration.OptimizeSize;
             #endif

example/unity/DemoApp/Assets/FlutterUnityIntegration/Editor/XCodePostBuild.cs

@@ -24,6 +24,7 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 
 using System.Collections.Generic;
 using System.IO;
+using System.Text.RegularExpressions;
 
 using UnityEditor;
 using UnityEditor.iOS.Xcode;
@@ -323,7 +324,9 @@ private static void EditUnityAppControllerMM(string path)
             inScope |= line.Contains("- (void)startUnity:");
             markerDetected |= inScope && line.Contains(TouchedMarker);
 
-            if (inScope && line.Trim() == "}")
+            //Find the end of the startUnity function, a } without any indentation.  (regex: starts with } followed by any whitespace)
+            //Avoid indentation before } as newer unity versions include an if-statement inside this function.
+            if (inScope && Regex.Match(line, @"^}(\s)*$").Success)
             {
                 inScope = false;
 
@@ -333,6 +336,7 @@ private static void EditUnityAppControllerMM(string path)
                 }
                 else
                 {
+                    //Add a UnityReady notification at the end of the startUnity function.
                     return new string[]
                     {
                         "    // Modified by " + TouchedMarker,