Rewrite array accesses as part of dereferences

Stops at any array accesses on external pointers and tries to rewrite
both the array access and the member dereference if any, in one shot.
With this commit, the following C code is rewritten properly into a
single bpf_probe_read call.

int test(struct pt_regs *ctx, const struct qstr *name) {
    return name->name[1];
}

Based on Yonghong Song's code.