Explicitly wake the main loop when scheduling a React revision merge (#57245)

Summary:
Pull Request resolved: #57245

Changelog: [IOS][FIXED] Add an explicit wake up call to the main loop hen scheduling a React revision merge

I could be possible that on idle screens the run loop is asleep, so without an explicit wake up call, the scheduled merges aren't processed.

This diff adds an explicit wake call when a merge is scheduled.

Reviewed By: rubennorte

Differential Revision: D108610347

fbshipit-source-id: 5ea02237b2152072b49a29482617fabbee34259f

Author: j-piasecki

packages/react-native/React/Fabric/RCTSurfacePresenter.mm

@@ -349,8 +349,16 @@ - (void)schedulerShouldMergeReactRevision:(SurfaceId)surfaceId
     return;
   }
 
-  std::lock_guard<std::mutex> lock(_pendingReactRevisionMergesMutex);
-  _pendingReactRevisionMerges.insert(surfaceId);
+  bool needsWake = false;
+  {
+    std::lock_guard<std::mutex> lock(_pendingReactRevisionMergesMutex);
+    needsWake = _pendingReactRevisionMerges.empty();
+    _pendingReactRevisionMerges.insert(surfaceId);
+  }
+
+  if (needsWake) {
+    CFRunLoopWakeUp(CFRunLoopGetMain());
+  }
 }
 
 - (void)_mergeReactRevisionForSurfaceId:(SurfaceId)surfaceId