Port xref-tests to master branch

Port xref-tests to master branch

Also, add a test to make this problem less likely in the future.
* test/Makefile.in (check-no-automated-subdir): New rule.
(check, check-expensive, check-maybe): Depend on it.
* test/automated/data/xref/file1.txt: Rename to ...
* test/data/xref/file1.txt: ... here.
* test/automated/data/xref/file2.txt: Rename to ...
* test/data/xref/file2.txt: ... here.
* test/automated/xref-tests.el: Rename to ...
* test/lisp/progmodes/xref-tests.el: ... here.
(xref-tests-data-dir): Use EMACS_TEST_DIRECTORY.