By exposing an ALL_TESTS list in defs.bzl we can make sure all packetimpact
users get to agree on the list of all tests. A defect in this approach is that
we have to keep a list of packetimpact_testbench rules in the BUILD file. An
helper validate_all_tests has been added to help keep BUILD and .bzl files in
sync.
PiperOrigin-RevId: 337411839