selftests/bpf: add ability to filter programs in veristat

Add -f (--filter) argument which accepts glob-based filters for
narrowing down what BPF object files and programs within them should be
processed by veristat. This filtering applies both to comparison and
main (verification) mode.

Filter can be of two forms:
  - file (object) filter: 'strobemeta*'; in this case all the programs
    within matching files are implicitly allowed (or denied, depending
    if it's positive or negative rule, see below);
  - file and prog filter: 'strobemeta*/*unroll*' will further filter
    programs within matching files to only allow those program names that
    match '*unroll*' glob.

As mentioned, filters can be positive (allowlisting) and negative
(denylisting). Negative filters should start with '!': '!strobemeta*'
will deny any filename which basename starts with "strobemeta".

Further, one extra special syntax is supported to allow more convenient
use in practice. Instead of specifying rule on the command line,
veristat allows to specify file that contains rules, both positive and
negative, one line per one filter. This is achieved with -f @<filepath>
use, where <filepath> points to a text file containing rules (negative
and positive rules can be mixed). For convenience empty lines and lines
starting with '#' are ignored. This feature is useful to have some
pre-canned list of object files and program names that are tested
repeatedly, allowing to check in a list of rules and quickly specify
them on the command line.

As a demonstration (and a short cut for nearest future), create a small
list of "interesting" BPF object files from selftests/bpf and commit it
as veristat.cfg. It currently includes 73 programs, most of which are
the most complex and largest BPF programs in selftests, as judged by
total verified instruction count and verifier states total.

If there is overlap between positive or negative filters, negative
filter takes precedence (denylisting is stronger than allowlisting). If
no allow filter is specified, veristat implicitly assumes '*/*' rule. If
no deny rule is specified, veristat (logically) assumes no negative
filters.

Also note that -f (just like -e and -s) can be specified multiple times
and their effect is cumulative.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220921164254.3630690-5-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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