2/3 Make interop WebView component Bridgeless compatible, and make uiManager addUIBlock migration easier

Summary:
Changelog: [iOS] Add `_viewRegistry_DEPRECATED addUIBlock`  to replace `uiManager addUIBlock` for Fabric migration

Allow people to directly replace `uiManager addUIBlock` with `_viewRegistry_DEPRECATED addUIBlock` when they migrate the method in RCTViewManagers.

Currently we add an if check in the RCTViewManager, which makes migration a bit harder for OSS.
```
  if (self.bridge) {
    [self.bridge.uiManager addUIBlock:^(__unused RCTUIManager *uiManager, NSDictionary<NSNumber *, UIView *> *viewRegistry) {
      work();
    }];
  } else {
    RCTExecuteOnMainQueue(work);
  }
```

Reviewed By: sammy-SC

Differential Revision: D34532609

fbshipit-source-id: 19647fea03be8fd71d8f46dfe216275894d8165c

React/Base/RCTBridgeModule.h

@@ -437,6 +437,8 @@ typedef NSURL * (^RCTBridgelessBundleURLGetter)(void);
 
 typedef UIView * (^RCTBridgelessComponentViewProvider)(NSNumber *);
 
+typedef void (^RCTViewRegistryUIBlock)(RCTViewRegistry *viewRegistry);
+
 /**
  * A class that allows NativeModules to query for views, given React Tags.
  */
@@ -445,6 +447,7 @@ typedef UIView * (^RCTBridgelessComponentViewProvider)(NSNumber *);
 - (void)setBridgelessComponentViewProvider:(RCTBridgelessComponentViewProvider)bridgelessComponentViewProvider;
 
 - (UIView *)viewForReactTag:(NSNumber *)reactTag;
+- (void)addUIBlock:(RCTViewRegistryUIBlock)block;
 @end
 
 typedef void (^RCTBridgelessJSModuleMethodInvoker)(

React/Base/RCTViewRegistry.m

@@ -42,4 +42,28 @@
   return view;
 }
 
+- (void)addUIBlock:(RCTViewRegistryUIBlock)block
+{
+  if (!block) {
+    return;
+  }
+
+  __weak __typeof(self) weakSelf = self;
+  if (_bridge) {
+    [_bridge.uiManager addUIBlock:^(RCTUIManager *uiManager, NSDictionary<NSNumber *, UIView *> *viewRegistry) {
+      __typeof(self) strongSelf = weakSelf;
+      if (strongSelf) {
+        block(strongSelf);
+      }
+    }];
+  } else {
+    RCTExecuteOnMainQueue(^{
+      __typeof(self) strongSelf = weakSelf;
+      if (strongSelf) {
+        block(strongSelf);
+      }
+    });
+  }
+}
+
 @end