Pass new DemoAssetManager with open and readText methods.

Change-Id: I4b58c250e76f6d41e794087ff3b467fc61c88eca

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/di/NetworkModule.kt

@@ -32,6 +32,7 @@ import kotlinx.serialization.json.Json
 import okhttp3.Call
 import okhttp3.OkHttpClient
 import okhttp3.logging.HttpLoggingInterceptor
+import java.io.InputStream
 import javax.inject.Singleton
 
 @Module
@@ -48,7 +49,10 @@ internal object NetworkModule {
     @Singleton
     fun providesDemoAssetManager(
         @ApplicationContext context: Context,
-    ): DemoAssetManager = DemoAssetManager(context.assets::open)
+    ): DemoAssetManager = object : DemoAssetManager {
+        override fun open(fileName: String): InputStream = context.assets.open(fileName)
+        override fun readText(fileName: String): String = context.assets.open(fileName).bufferedReader().use { it.readText() }
+    }
 
     @Provides
     @Singleton