[general] moving ios and android project under ./platform folder

benchmark/android/build.gradle

@@ -0,0 +1,21 @@
+// Top-level build file where you can add configuration options common to all sub-projects/modules.
+buildscript {
+    repositories {
+       google()
+       jcenter()
+    }
+    dependencies {
+        classpath 'com.android.tools.build:gradle:3.5.3'
+    }
+}
+
+allprojects {
+    repositories {
+        google()
+        jcenter()
+    }
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}