Add Fabric support

[okwasniewski]

Summary:

Introduce Fabric support for iOS and Android. #380

iOS Changes:

• Setup codegen spec in flow
• Move requireNativeComponent to separate file
• Update podspec file
• Add codegenConfig in package.json
• Ensure backwards compatibility
• iOS Implementation

Android Changes:

• Configure gradle files
• Implement / extend the generated native interfaces
• Ensure backwards compatibility by splitting implementations into two folders.

Related PRs:

• Add fabric on iOS #400
• Add fabric on Android #402

Test Plan:

Currently updating example app to RN 0.70 is blocked, tracked here: #408

Test plan for RN <0.70:

Android

1. Set newArchEnabled to true inside example/android/gradle.properties
2. Add this line in example/android/app/src/main/jni/Android.mk file.

+ include $(NODE_MODULES_DIR)/@react-native-community/slider/android/build/generated/source/codegen/jni/Android.mk
include $(CLEAR_VARS)

In the same file above, go to the LOCAL_SHARED_LIBRARIES setting and add the following line:

    libreact_codegen_rncore \
+   libreact_codegen_ReactSlider \
    libreact_debug \

3. Update example/android/app/src/main/jni/MainComponentsRegistry.cpp

#include <react/renderer/components/rncore/ComponentDescriptors.h>
+ #include <react/renderer/components/ReactSlider/ComponentDescriptors.h>

...

MainComponentsRegistry::sharedProviderRegistry() {
  auto providerRegistry = CoreComponentsRegistry::sharedProviderRegistry();

  // Custom Fabric Components go here. You can register custom
  // components coming from your App or from 3rd party libraries here.
  //
  // providerRegistry->add(concreteComponentDescriptorProvider<
  //        AocViewerComponentDescriptor>());
+ providerRegistry->add(concreteComponentDescriptorProvider<RNCSliderComponentDescriptor>());

  return providerRegistry;
}

Then, to launch the project run:

npm run install && npm run example-android

iOS

Install pods using a flag

RCT_NEW_ARCH_ENABLED=1 pod install

Run the app

npm run example-ios

[thymikee]

[michalchudziak]

Good job!