Mark ShadowNode::Shared as deprecated and replace all usages (#52393)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52393

## Changelog:
[General][Deprecated] - ShadowNode::Shared is now deprecated. Use `std::shared_ptr<const ShadowNode>` instead.

- Mark ShadowNode::Shared as deprecated in ShadowNode.h
- Replace all uses of ShadowNode::Shared with std::shared_ptr<const ShadowNode>.

This continues the systematic effort to remove ShadowNode type aliases in favor of explicit standard library types for improved code clarity and maintainability.

Reviewed By: christophpurrer

Differential Revision: D77650696

fbshipit-source-id: b4769e2a1e39f49d14d5927be105487ecf69fa3f