android build: Upgrade Android Gradle Plugin to v3.5.2.

Release notes here:
  https://developer.android.com/studio/releases/gradle-plugin#3-5-0
No major potentially-incompatible changes identified there.

Part of the RN v0.61 -> v0.62 changes to the template app [1],
corresponding to facebook/react-native@6aae8e075 and
facebook/react-native@b41b5ce8a. Probably best to do it before the
main upgrade commit.

[1] https://react-native-community.github.io/upgrade-helper/?from=0.61.5&to=0.62.2

android/build.gradle

@@ -28,7 +28,7 @@ buildscript {
     }
     dependencies {
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-        classpath 'com.android.tools.build:gradle:3.5.0'
+        classpath 'com.android.tools.build:gradle:3.5.2'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files