Android: Enable apps to provide a custom configuration to Fresco

Summary:
The `FrescoModule` supports providing a custom image pipeline configuration. This module is created by `MainReactPackage` but `MainReactPackage` doesn't expose any way to customize the Fresco configuration. This change adds a parameter to `MainReactPackage`'s constructor so that the `FrescoModule`'s configuration can be customized by the app. A couple of design choices were made in this change:
  - `MainReactPackage`'s new constructor parameter is a `MainPackageConfig`. Introducing `MainPackageConfig` enables `MainReactPackage` to nicely support new optional configuration options in the future. Imagine the alternative of each optional configuration being a separate parameter to the `MainReactPackage` constructor.
  - `FrescoModule` exposes its default configuration as a builder object through the `getDefaultConfigBuilder` method. This enables app's to start with `FrescoModule`'s default configuration and then modify it.

**Test plan (required)**

Verified that passing a custom config based on React Nati
Closes https://github.com/facebook/react-native/pull/10906

Differential Revision: D4237054

Pulled By: mkonicek

fbshipit-source-id: 8a62a6f0e77ca5f6d35238950094686756262196

ReactAndroid/src/main/java/com/facebook/react/shell/MainPackageConfig.java

@@ -0,0 +1,42 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.shell;
+
+import com.facebook.imagepipeline.core.ImagePipelineConfig;
+
+/**
+ * Configuration for {@link MainReactPackage}
+ */
+public class MainPackageConfig {
+
+  private ImagePipelineConfig mFrescoConfig;
+
+  private MainPackageConfig(Builder builder) {
+    mFrescoConfig = builder.mFrescoConfig;
+  }
+
+  public ImagePipelineConfig getFrescoConfig() {
+    return mFrescoConfig;
+  }
+
+  public static class Builder {
+
+    private ImagePipelineConfig mFrescoConfig;
+
+    public Builder setFrescoConfig(ImagePipelineConfig frescoConfig) {
+      mFrescoConfig = frescoConfig;
+      return this;
+    }
+
+    public MainPackageConfig build() {
+      return new MainPackageConfig(this);
+    }
+  }
+}