eBPF custom maps should support find/lookup from BPF programs

### Describe the feature you'd like supported

eBPF extensible maps should support find/lookup from BPF programs.

On Linux, for example, it is idiomatic for BPF programs to do this:

```
SEC("xdp")
int xsk_redir_prog(struct xdp_md *ctx)
{
__u32 index = ctx->rx_queue_index;

if (bpf_map_lookup_elem(&xsks_map, &index))
return bpf_redirect_map(&xsks_map, index, 0);
return XDP_PASS;
}
```

### Proposed solution

Allow the find postprocessing routine to observe usage with `EBPF_MAP_OPERATION_HELPER`. This should be opt-in by each extension, as it would otherwise be a breaking change from today's eBPF runtime behavior.

### Additional context

_No response_