Browser-side JS: File System API vs File System Access API?

There was a File System API but shown as deprecated now:
https://developer.mozilla.org/en-US/docs/Web/API/Window/requestFileSystem

There is now another, File System Access API:
https://developer.mozilla.org/en-US/docs/Web/API/File_System_Access_API

What happened to the old API and why was it discontinued? Should the new File System Access API be stable in all common browsers?