Split up the Microsoft.ReactNative.dll into two DLLs: Core and UWP

Task: Split up the Microsoft.ReactNative.dll into two DLLs: Core and UWP

Summary

Introduce a new Microsoft.ReactNative.Uwp.dll that has all the UWP specific code. It includes the ReactApplication, native modules, ViewManagers and any other XAML-based code. The Microsoft.ReactNative.dll is kept as a relatively thin wrapper around the ReactNative code and exposes it through the ABI-safe API.

Motivation

There are several scenarios we would like to address:

• Use Microsoft.ReactNative.dll for non-XAML based UI.
• Use Microsoft.ReactNative.dll for UWP and Win32 applications.
• Write internal and external NativeModules and TurboModules using the same ABI-safe API.

Basic examples

• Generate TurboModules based on ReactNative spec files that have the same shape for internal and external code that use the same ABI-safe API.
• Microsoft Office applications require to define its own UI ViewManages based on non-XAML components.

Open Questions

• Where should we have the UI shadow tree: in Microsoft.ReactNative.dll or Microsoft.ReactNative.Uwp.dll? Ideally it should be in the common shared core Microsoft.ReactNative.dll.
• Should the the new "Core DLL" Microsoft.ReactNative.dll support plugable JavaScript engines (Hermes, V8, Chakra) or it must wrap only one of them?