rat: tuple: improve latex pretty-printing
Instead of `E \mid F`, whose size does not depend on the size of its argument, use `\left. E \middle| \right.`. Suggested by Alexandre Duret-Lutz. * vcsn/core/rat/printer.hh, vcsn/core/rat/printer.hxx: here. * tests/bin/test.py: Always print the expected/effective paragraphs. Even if they are redundant for single line changes, they enable the use of update-tests. * tests/python/transducer.py: Update expectations.