Add support for distributed registration of Fabric Components with Dynamic Libraries

Summary:
With dynamic frameworks, we can't use floating C functions.

The way in which dynamic frameworks work is that they need to be self contained. They are built in isolation so that other frameworks can be linked against them to solve their dependencies.

Currently, when working with 3rd party libraries, we are Codegenerating a RCTThirdPartyComponentProvider which tries to invoke floating C functions that are defined in other modules. React-RCTFabric has no visibility on those modules, therefore it fails building.

The implemented solution exclude the generation of those symbols and leverage a the Objective-C runtime to automatically register libraries when they are loaded.

**This mechanism is applied ONLY when the flag RCT_DYNAMIC_FRAMEWORKS is turned on.** There will be no impact on internal meta apps, nor on any apps that are not using Dynamic Frameworks.

This change requires a small migration in all the Fabric components libraries that wants to support dynamic frameworks. They have to implement a
```
+ (void)load
{
  [super load];
}
```
method in their ComponentView.

Not to slow down the adoption of the new architecture, waiting for a migration in the ecosystem, the next diff introduce a secondary, declarative loading mechanism for Fabric Components, which follows the same approach used by TurboModules.

## Changelog:
[iOS][Changed] - Add support for distributed registration of  Fabric Components with Dynamic Libraries.

Notes that this change is NOT breaking as dynamic frameworks were not working before in the New Architecture. Static Libraries and Static Frameworks continue working as usual.

Differential Revision: D45605441

fbshipit-source-id: 6ff81fe5af8763c19b86d7b04761c556fac51e79

Author: cipolleschi

packages/react-native-codegen/src/generators/components/GenerateThirdPartyFabricComponentsProviderH.js

@@ -36,8 +36,12 @@ extern "C" {
 
 Class<RCTComponentViewProtocol> RCTThirdPartyFabricComponentsProvider(const char *name);
 
+#ifndef RCT_DYNAMIC_FRAMEWORKS
+
 ${lookupFuncs}
 
+#endif
+
 #ifdef __cplusplus
 }
 #endif

packages/react-native-codegen/src/generators/components/GenerateThirdPartyFabricComponentsProviderObjCpp.js

@@ -34,7 +34,9 @@ const FileTemplate = ({lookupMap}: {lookupMap: string}) => `
 
 Class<RCTComponentViewProtocol> RCTThirdPartyFabricComponentsProvider(const char *name) {
   static std::unordered_map<std::string, Class (*)(void)> sFabricComponentsClassMap = {
+    #ifndef RCT_DYNAMIC_FRAMEWORKS
 ${lookupMap}
+    #endif
   };
 
   auto p = sFabricComponentsClassMap.find(name);

packages/react-native-codegen/src/generators/components/__tests__/__snapshots__/GenerateThirdPartyFabricComponentsProviderH-test.js.snap

@@ -23,6 +23,8 @@ extern \\"C\\" {
 
 Class<RCTComponentViewProtocol> RCTThirdPartyFabricComponentsProvider(const char *name);
 
+#ifndef RCT_DYNAMIC_FRAMEWORKS
+
 Class<RCTComponentViewProtocol> NoPropsNoEventsComponentCls(void) __attribute__((used)); // NO_PROPS_NO_EVENTS
 Class<RCTComponentViewProtocol> InterfaceOnlyComponentCls(void) __attribute__((used)); // INTERFACE_ONLY
 Class<RCTComponentViewProtocol> BooleanPropNativeComponentCls(void) __attribute__((used)); // BOOLEAN_PROP
@@ -55,6 +57,8 @@ Class<RCTComponentViewProtocol> ExcludedAndroidComponentCls(void) __attribute__(
 
 Class<RCTComponentViewProtocol> MultiFileIncludedNativeComponentCls(void) __attribute__((used)); // EXCLUDE_IOS_TWO_COMPONENTS_DIFFERENT_FILES
 
+#endif
+
 #ifdef __cplusplus
 }
 #endif

packages/react-native-codegen/src/generators/components/__tests__/__snapshots__/GenerateThirdPartyFabricComponentsProviderObjCpp-test.js.snap

@@ -21,6 +21,7 @@ Map {
 
 Class<RCTComponentViewProtocol> RCTThirdPartyFabricComponentsProvider(const char *name) {
   static std::unordered_map<std::string, Class (*)(void)> sFabricComponentsClassMap = {
+    #ifndef RCT_DYNAMIC_FRAMEWORKS
 
     {\\"NoPropsNoEventsComponent\\", NoPropsNoEventsComponentCls}, // NO_PROPS_NO_EVENTS
 
@@ -80,6 +81,7 @@ Class<RCTComponentViewProtocol> RCTThirdPartyFabricComponentsProvider(const char
 
 
     {\\"MultiFileIncludedNativeComponent\\", MultiFileIncludedNativeComponentCls}, // EXCLUDE_IOS_TWO_COMPONENTS_DIFFERENT_FILES
+    #endif
   };
 
   auto p = sFabricComponentsClassMap.find(name);

packages/react-native/React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm

@@ -13,6 +13,7 @@
 
 #import <React/RCTAssert.h>
 #import <React/RCTBorderDrawing.h>
+#import <React/RCTComponentViewFactory.h>
 #import <React/RCTConversions.h>
 #import <react/renderer/components/view/ViewComponentDescriptor.h>
 #import <react/renderer/components/view/ViewEventEmitter.h>
@@ -30,6 +31,13 @@ @implementation RCTViewComponentView {
   NSSet<NSString *> *_Nullable _propKeysManagedByAnimated_DO_NOT_USE_THIS_IS_BROKEN;
 }
 
+#ifdef RCT_DYNAMIC_FRAMEWORKS
++ (void)load
+{
+  [RCTComponentViewFactory.currentComponentViewFactory registerComponentViewClass:self];
+}
+#endif
+
 - (instancetype)initWithFrame:(CGRect)frame
 {
   if (self = [super initWithFrame:frame]) {

packages/react-native/scripts/cocoapods/new_architecture.rb

@@ -67,6 +67,17 @@ def self.modify_flags_for_new_architecture(installer, is_new_arch_enabled)
                 end
             end
 
+            # Set "RCT_DYNAMIC_FRAMEWORKS=1" if pod are installed with USE_FRAMEWORKS=dynamic
+            # This helps with backward compatibility.
+            if pod_name == 'React-RCTFabric' && ENV['USE_FRAMEWORKS'] == 'dynamic'
+                Pod::UI.puts "Adding RCT_DYNAMIC_FRAMEWORKS=1 to React-RCTFabric".yellow
+                rct_dynamic_framework_flag = " -DRCT_DYNAMIC_FRAMEWORKS=1"
+                target_installation_result.native_target.build_configurations.each do |config|
+                    prev_build_settings = config.build_settings['OTHER_CPLUSPLUSFLAGS'] != nil ? config.build_settings['OTHER_CPLUSPLUSFLAGS'] : "$(inherithed)"
+                    config.build_settings['OTHER_CPLUSPLUSFLAGS'] = prev_build_settings + rct_dynamic_framework_flag
+                end
+            end
+
             target_installation_result.native_target.build_configurations.each do |config|
                 if config.name == "Release"
                     current_flags = config.build_settings['OTHER_CPLUSPLUSFLAGS'] != nil ? config.build_settings['OTHER_CPLUSPLUSFLAGS'] : "$(inherited)"

packages/rn-tester/NativeComponentExample/ios/RNTMyNativeViewComponentView.mm

@@ -7,6 +7,7 @@
 
 #import "RNTMyNativeViewComponentView.h"
 
+#import <React/RCTComponentViewFactory.h>
 #import <react/renderer/components/AppSpecs/ComponentDescriptors.h>
 #import <react/renderer/components/AppSpecs/EventEmitters.h>
 #import <react/renderer/components/AppSpecs/Props.h>
@@ -28,6 +29,14 @@ + (ComponentDescriptorProvider)componentDescriptorProvider
   return concreteComponentDescriptorProvider<RNTMyNativeViewComponentDescriptor>();
 }
 
+// Load is not invoked if it is not defined, therefore, we must ask to update this.
+// See the Apple documentation: https://developer.apple.com/documentation/objectivec/nsobject/1418815-load?language=objc
+// "[...] but only if the newly loaded class or category implements a method that can respond."
++ (void)load
+{
+  [super load];
+}
+
 - (instancetype)initWithFrame:(CGRect)frame
 {
   if (self = [super initWithFrame:frame]) {