selftests/bpf: Add BTF repeated field count overflow test

selftests/bpf: Add BTF repeated field count overflow test

Add a raw BTF test that exercises repeated special-field expansion with a
large array count. The compact element layout keeps the array byte size
representable while the repeated field count overflows the old u32 capacity
calculation in btf_repeat_fields().

Signed-off-by: Paul Moses <p@1g4.org>
Link: https://lore.kernel.org/bpf/SzebdWqm2zREZBf8Tc5Kc-JDWbh9nBztnk4PUu5kRSD1OOdr_ESVTt__2Hd3-lClr47jIjJCXfOH0RHsMpjjpEUh_R2v30nh3T1IXNT6Pbo=@1g4.org
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>