selftests/bpf: test bpf_get_func_arg() for tp_btf

selftests/bpf: test bpf_get_func_arg() for tp_btf

Test bpf_get_func_arg() and bpf_get_func_arg_cnt() for tp_btf. The code
is most copied from test1 and test2.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260121044348.113201-3-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>