libbpf: Introduce bpf_{btf,link,map,prog}_get_info_by_fd()

These are type-safe wrappers around bpf_obj_get_info_by_fd(). They
found one problem in selftests, and are also useful for adding
Memory Sanitizer annotations.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230214231221.249277-2-iii@linux.ibm.com