adf1c7915d
This is a new `DataSource` that can be used to read from a `FileDescriptor`. Limitations: - The provided file descriptor must be seekable via lseek. - There's no way to duplicate a file descriptor with an independent position (it would be necessary instead for the app to provide a new FD). Therefore this implementation will only work if there's one open data source for a given file descriptor at a time. PiperOrigin-RevId: 649443584