Ian Macphail

@livecode-vulcan review ok 4e8ac6a

@runrevmark GetFileSize could return an incorrect value if the file was opened in update mode. Aside from that I don't see any other problems 😉

@runrevmark shouldn't that be `max(actual_file_size, file_ptr + buffered_write_size)` as the buffered_write_size won't affect the size unless it goes beyond the current EOF? Alternatively you could just flush the buffer before...

@runrevmark I've revised this PR so that platform-specific code is moved to a seperate source file, and implemented the fallback for Android < 26. I've also abstracted the hardwarebuffer stuff...