Let the Yoga sample app compile

Summary:
The sample app is really old and has a lot of legacy code. Here I'm refreshing it a bit.
Will do another pass later (perhaps rewrite it in Kotlin?).

Reviewed By: mdvacca

Differential Revision: D45694414

fbshipit-source-id: 36a84609b0dcf5b4a5237da900f665e4eb7895a5

gradle.properties

@@ -7,6 +7,8 @@
 
 # Project-wide Gradle settings.
 
+android.useAndroidX=true
+
 org.gradle.jvmargs=-Xmx1536M
 
 VERSION_NAME=1.19.0