Tests for the ".emit_strings" functionality in the BTF dumper.

When this mode is turned on, "emit_zeroes" and "compact" have no effect,
and embedded NUL characters always terminate printing of an array.

Signed-off-by: Blake Jones <blakejones@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250603203701.520541-2-blakejones@google.com