Define modules and use modular headers to simplify Swift integration (#…

…39148)

Summary:
Pull Request resolved: #39148

This change adds another `DEFINES_MODULE` to React-ImageManager which is required to integrate with Swift.

## Changelog:
[Internal] - Add Defines modules for React-ImageManager.

## Facebook:
This work is required to collaborate with Expo on ExpoModules

Reviewed By: dmytrorykun

Differential Revision: D48648153

fbshipit-source-id: b06f049be2aedc9fb1ca4744fde0dda88cb74ece

packages/react-native/ReactCommon/react/renderer/imagemanager/platform/ios/React-ImageManager.podspec

@@ -57,7 +57,8 @@ Pod::Spec.new do |s|
   s.pod_target_xcconfig  = {
     "USE_HEADERMAP" => "NO",
     "HEADER_SEARCH_PATHS" => header_search_paths.join(" "),
-    "CLANG_CXX_LANGUAGE_STANDARD" => "c++17"
+    "CLANG_CXX_LANGUAGE_STANDARD" => "c++17",
+    "DEFINES_MODULE" => "YES",
   }
 
   s.dependency "RCT-Folly/Fabric"