Rename flag IS_DOGFOOD to IS_STUDIO.

The flag is only set when building from Android Studio... and is never
used for dogfood.

Test: local
Change-Id: I898d585f4558c2437f0152ef102bea59c351f80b

src/com/android/launcher3/model/ModelUtils.java

@@ -97,7 +97,7 @@ public class ModelUtils {
                         return Integer.compare(lhs.screenId, rhs.screenId);
                     }
                     default:
-                        if (FeatureFlags.IS_DOGFOOD_BUILD) {
+                        if (FeatureFlags.IS_STUDIO_BUILD) {
                             throw new RuntimeException(
                                     "Unexpected container type when sorting workspace items.");
                         }