Fix Android build sequencing

Summary:
The native libraries are compiled outside of the usual Android build flow using separate CLI task. Because of that, shared native libraries may not exist when AAR is bundled, resulting in weird sequencing issues.

This change updates gradle dependency graph, executing RN native build before Android part (as it is done in RNTester already).

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D29209249

fbshipit-source-id: 36386c78996b1cd9b1731735e36e571199e9e81b

ReactAndroid/build.gradle

@@ -470,11 +470,7 @@ android {
         }
     }
 
-    tasks.withType(JavaCompile) {
-        compileTask ->
-            compileTask.dependsOn(packageReactNdkLibs)
-    }
-
+    preBuild.dependsOn(packageReactNdkLibs)
     clean.dependsOn(cleanReactNdkLib)
 
     lintOptions {