Make Hermes the default engine on Android. (#34049)

Summary:
Pull Request resolved: #34049

This just flips the switch for having Hermes on by default
on new projects for React Native.

Changelog:
[Android] [Changed] - Make Hermes the default engine on Android

Reviewed By: neildhar, jpporto

Differential Revision: D37354079

fbshipit-source-id: cb0391eb3927d13432e7d4b9efef7b8812938a98

template/android/app/build.gradle

@@ -78,7 +78,7 @@ import com.android.build.OutputFile
  */
 
 project.ext.react = [
-    enableHermes: false,  // clean and rebuild if changing
+    enableHermes: true,  // clean and rebuild if changing
 ]
 
 apply from: "../../node_modules/react-native/react.gradle"