Fix sample app build

Summary:
Two fixes included in this one. The debug flag is obvious, the annotations
less so. I'll try and find the right place to document this, but the reason
we need this here is because we reflect on `Prop.class`, so these need to be
available at runtime.

Reviewed By: jknoxville

Differential Revision: D9766713

fbshipit-source-id: 269b5a60c0df644f4fda0ea289ef9dc392ee352b

android/sample/build.gradle

@@ -27,7 +27,7 @@ dependencies {
     // Litho
     implementation deps.lithoCore
     implementation deps.lithoWidget
-    compileOnly deps.lithoAnnotations
+    implementation deps.lithoAnnotations
     annotationProcessor deps.lithoProcessor
 
     // Third-party

android/sample/src/main/java/com/facebook/flipper/sample/FlipperSampleApplication.java

@@ -4,6 +4,7 @@ package com.facebook.flipper.sample;
 
 import android.app.Application;
 import android.content.Context;
+import com.facebook.litho.config.ComponentsConfiguration;
 import com.facebook.soloader.SoLoader;
 import com.facebook.sonar.android.AndroidSonarClient;
 import com.facebook.sonar.core.SonarClient;
@@ -39,6 +40,9 @@ public class FlipperSampleApplication extends Application {
     .writeTimeout(10, TimeUnit.MINUTES)
     .build();
 
+    // Normally, you would want to make this dependent on a BuildConfig flag, but
+    // for this demo application we can safely assume that you always want to debug.
+    ComponentsConfiguration.isDebugModeEnabled = true;
     LithoSonarDescriptors.add(descriptorMapping);
     client.addPlugin(new InspectorSonarPlugin(this, descriptorMapping));
     client.addPlugin(networkPlugin);