This introduces new API for fd copying and modifies php_stream_copy_to_stream_ex to use it. The implementation is separated for various platforms and the end result have couple of implications:

• sendfile is used for copying file to generic fd (e.g. sockets) on linux, bsd, macos and solaris (it uses sendfilev actually)
• splice is used for copying between generic fds (e.g. sockets) on linux
• copy_file_range should get used on alpine linux with directly using syscall (as musl does not seem to implement it)
• copy_file_range is used in the loop so it is used multiple times for files bigger than 2GB on linux
• file mmap for copying is removed as it allowed crashing PHP when another process modified mapped file - this was used as a fallback for file copying which is no longer needed and sendfile is used for file copying to stream which should be also more effective
• TransmitFile is used on Windows for copying file to generic fd (socket)
• file to file copying was also optimized on Windows with use of ReadFile and WriteFile.