bpf: generalize is_branch_taken to handle all conditional jumps in one place

bpf: generalize is_branch_taken to handle all conditional jumps in one place

Make is_branch_taken() a single entry point for branch pruning decision
making, handling both pointer vs pointer, pointer vs scalar, and scalar
vs scalar cases in one place. This also nicely cleans up check_cond_jmp_op().

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231102033759.2541186-15-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>