Make sure to set BPF_F_TEST_SANITY_STRICT program flag by default across
most verifier tests (and a bunch of others that set custom prog flags).

There are currently two tests that do fail validation, if enforced
strictly: verifier_bounds/crossing_64_bit_signed_boundary_2 and
verifier_bounds/crossing_32_bit_signed_boundary_2. To accommodate them,
we teach test_loader a flag negation:

__flag(!<flagname>) will *clear* specified flag, allowing easy opt-out.

We apply __flag(!BPF_F_TEST_SANITY_STRICT) to these to tests.

Also sprinkle BPF_F_TEST_SANITY_STRICT everywhere where we already set
test-only BPF_F_TEST_RND_HI32 flag, for completeness.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231112010609.848406-12-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>