You are a software engineer working on a large$-$scale web application deployed on Google App Engine. The application allows users to upload and share multimedia files such as images, videos, and documents. As part of the application's functionality, users can perform various operations on their uploaded files, including editing, deleting, and sharing with other users. Describe how you would implement data mutation operations such as editing and deleting files stored in the Google File System. Discuss the use of appropriate APIs or libraries provided by Google Cloud Platform $($GCP$)$ to perform CRUD $($Create$,$ Read, Update, Delete$)$ operations on files. Explain how you would handle concurrency and consistency issues when multiple users perform concurrent mutations on the same file.