selftests/bpf: Verify copy_register_state() preserves parent/live fields

A testcase to check that verifier.c:copy_register_state() preserves
register parentage chain and livness information.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230106142214.1040390-3-eddyz87@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>