Cleanup of the test file for cperl-mode

Cleanup of the test file for cperl-mode

* test/lisp/progmodes/cperl-mode-tests.el
(cperl--run-test-cases): New macro, factored out from various
indentation / rewriting tests.  Contains documentation of the
format used by the cperl-mode-resources files.
(cperl-test-bug-19709): Replace 'next-line' by 'forward-line'.
(cperl-test-indent-exp),
(cperl-test-indent-styles),
(cperl-test-bug-30393): Use the new macro.
(cperl-test-bug-19709): Make fit for Emacs 26.
(cperl-test-indent-styles): Skip for Perl mode (bug#44561).