Move ReactHost to com.facebook.react (#39769)

Summary:
Pull Request resolved: facebook/react-native#39769

Move ReactHost to com.facebook.react

bypass-github-export-checks

changelog: [internal] internal

Reviewed By: javache

Differential Revision: D49834870

fbshipit-source-id: 2cfdd34297399115457424f0ba1279fd477da4a1

Original: facebook/react-native@7a44bd5

Author: mdvacca

template/template/android/app/src/main/java/com/helloworld/MainApplication.kt

@@ -3,14 +3,14 @@ package com.helloworld
 import android.app.Application
 import com.facebook.react.PackageList
 import com.facebook.react.ReactApplication
+import com.facebook.react.ReactHost
 import com.facebook.react.ReactNativeHost
 import com.facebook.react.ReactPackage
 import com.facebook.react.common.annotations.UnstableReactNativeAPI
 import com.facebook.react.defaults.DefaultNewArchitectureEntryPoint.load
 import com.facebook.react.defaults.DefaultReactHost
 import com.facebook.react.defaults.DefaultReactNativeHost
 import com.facebook.react.flipper.ReactNativeFlipper
-import com.facebook.react.interfaces.ReactHost
 import com.facebook.soloader.SoLoader
 
 @UnstableReactNativeAPI