Update to react-native 0.64 and enable Hermes

Summary:
allow-large-files

Per title. hermes enabled so that we can verify the hermes debugger works.

Reviewed By: passy

Differential Revision: D27229331

fbshipit-source-id: c2e45151b9d2097edc7e79f54eb89f9d110899d6

react-native/ReactNativeFlipperExample/android/build.gradle

@@ -9,17 +9,18 @@
 
 buildscript {
     ext {
-        buildToolsVersion = "29.0.2"
-        minSdkVersion = 16
+        buildToolsVersion = "29.0.3"
+        minSdkVersion = 21
         compileSdkVersion = 29
         targetSdkVersion = 29
+        ndkVersion = "20.1.5948944"
     }
     repositories {
         google()
         jcenter()
     }
     dependencies {
-        classpath("com.android.tools.build:gradle:3.5.3")
+        classpath("com.android.tools.build:gradle:4.1.0")
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files