Merge branch 'libbpf: Move CO-RE logic into separate file.'

Alexei Starovoitov says:

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From: Alexei Starovoitov <ast@kernel.org>

Split CO-RE processing logic from libbpf into separate file
with an interface that doesn't dependend on libbpf internal details.
As the next step relo_core.c will be compiled with libbpf and with the kernel.
The _internal_ interface between libbpf/CO-RE and kernel/CO-RE will be:
int bpf_core_apply_relo_insn(const char *prog_name, struct bpf_insn *insn,
			     int insn_idx,
			     const struct bpf_core_relo *relo,
			     int relo_idx,
			     const struct btf *local_btf,
			     struct bpf_core_cand_list *cands);
where bpf_core_relo and bpf_core_cand_list are simple types
prepared by kernel and libbpf.

Though diff stat shows a lot of lines inserted/deleted they are moved lines.
Pls review with diff.colorMoved.
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Signed-off-by: Andrii Nakryiko <andrii@kernel.org>