Fix native modules not being re-initialized on reload (#6159)

When calling `ReactNativeHost::ReloadInstance()`,
`ReactPackageProvider`s are not reiterated and thus not calling
`AddAttributedModules()`. As a consequence, the native modules that were
loaded the first time the app was loaded, no longer "exist" after
a reload.

Author: tido64

change/react-native-windows-2020-10-02-23-12-32-HEAD.json

@@ -0,0 +1,8 @@
+{
+  "type": "patch",
+  "comment": "Backport fix for native modules not being re-initialized on reload (#6159)",
+  "packageName": "react-native-windows",
+  "email": "[email protected]",
+  "dependentChangeType": "patch",
+  "date": "2020-10-02T21:12:32.521Z"
+}

vnext/Microsoft.ReactNative/ReactNativeHost.cpp

@@ -80,18 +80,16 @@ IAsyncAction ReactNativeHost::ReloadInstance() noexcept {
 
   auto turboModulesProvider = std::make_shared<TurboModulesProvider>();
 
-  if (!m_packageBuilder) {
-    m_packageBuilder = make<ReactPackageBuilder>(
-        modulesProvider,
+  m_packageBuilder = make<ReactPackageBuilder>(
+      modulesProvider,
 #ifndef CORE_ABI
-        viewManagersProvider,
+      viewManagersProvider,
 #endif
-        turboModulesProvider);
+      turboModulesProvider);
 
-    if (auto packageProviders = InstanceSettings().PackageProviders()) {
-      for (auto const &packageProvider : packageProviders) {
-        packageProvider.CreatePackage(m_packageBuilder);
-      }
+  if (auto packageProviders = InstanceSettings().PackageProviders()) {
+    for (auto const &packageProvider : packageProviders) {
+      packageProvider.CreatePackage(m_packageBuilder);
     }
   }