If a user picks a file which can't be opened for some reason, we should
still return the value, so client applications can report the error
along with the chosen filepath.
Adds new service FileSystemAccessServer which allows programs to
request a file descriptor for any file on the file system.
The user can be prompted to choose the path with a FilePicker, or the
path can be provided by the application which will show a MessageBox
showing the pid and name of the calling process and allows the user to
approve or deny the request.