selftests/bpf: Add dump type data tests to btf dump tests

Test various type data dumping operations by comparing expected
format with the dumped string; an snprintf-style printf function
is used to record the string dumped.  Also verify overflow handling
where the data passed does not cover the full size of a type,
such as would occur if a tracer has a portion of the 8k
"struct task_struct".
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1626362126-27775-4-git-send-email-alan.maguire@oracle.com