flutter: android: Upgrade gradle to 4.1.2 and cmake to 3.18.1

src/ui/flutter_app/android/app/build.gradle

@@ -73,6 +73,7 @@ android {
     externalNativeBuild {
         cmake {
             path "CMakeLists.txt"
+            version '3.18.1'
         }
     }
 }

src/ui/flutter_app/android/build.gradle

@@ -1,11 +1,14 @@
 buildscript {
     repositories {
+	    // Gradle 4.1 and higher include support for Google's Maven repo using
+        // the google() method. And you need to include this repo to download
+        // Android Gradle plugin 3.0.0 or higher.
         google()
         jcenter()
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.5.0'
+        classpath 'com.android.tools.build:gradle:4.1.2'
     }
 }
 

src/ui/flutter_app/android/gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.6.2-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-all.zip