Add a simple verifier test that requires deriving reg bounds for one
register from another register that's not a constant. This is
a realistic example of iterating elements of an array with fixed maximum
number of elements, but smaller actual number of elements.

This small example was an original motivation for doing this whole patch
set in the first place, yes.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231112010609.848406-14-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>