Fix AssetDatabase.AssetPathExists compatibility for Unity versions before 2023.1

[octo127]

Summary

This PR fixes a compilation error that occurs when using Unity versions prior to 2023.1 due to the use of AssetDatabase.AssetPathExists, which was added in Unity 2023.1.0a4.

Changes

• Added preprocessor directives to check Unity version
• For Unity 2023.1 and newer: Use AssetDatabase.AssetPathExists
• For older versions: Use AssetDatabase.LoadAssetAtPath<UnityEngine.Object>() != null as a fallback

Testing

• Verified that the functionality works correctly on both Unity 2022.3 and 2023.1+