Test that all IO routines on readers/writers/files work from remote locales

PR #24422 fixed a bug in which our seek() routines did not contain an on-clause before calling into the C IO routines, resulting in a segfault. This issue captures a desire to test all methods on fileReaders/fileWriters/files from a remote locale to ensure that other such bugs aren't lurking.

As an example of how such tests might look, here's a pattern that tests .seek() on a fileReader:

var infile = open("out.txt", ioMode.r);
on Locales[numLocales-1] {
  var myReader = infile.reader(locking=false);
  myReader.seek(2..#2);
  var i = myReader.read(int);
  writeln(i);
}