[orc-rt] Move the regression tests into test/regression (#208391)
Move the regression lit config and the existing tests into
test/regression/, and point the check-orc-rt suite there.
This is a first step towards consolidating tests and test infrastructure
under orc-rt/test. Upcoming commits will add a test tools directory, and
move the existing unit tests (under orc-rt/unittests) into
orc-rt/test/unit.