Add Unsafe based storage backend

Summary:
@public

Adds another version of property storage for `YogaNode`, using `sun.misc.Unsafe`.

Adopts the stub concept from Litho for `Unsafe`, as it is hidden by the Android SDK.

Reviewed By: pasqualeanatriello

Differential Revision: D9140103

fbshipit-source-id: a4b376eca341b724a00f873467ae8bf8eaac69f4

java/build.gradle

@@ -52,6 +52,7 @@ android {
 dependencies {
     compileOnly 'com.google.code.findbugs:jsr305:3.0.1'
     compileOnly project(':yoga:proguard-annotations')
+    compileOnly project(':yoga:stubs')
     implementation 'com.facebook.soloader:soloader:0.5.1'
     testImplementation 'junit:junit:4.12'
 }