Is there a way to map ctrl+h and backspace to different functions?

if I set `'c-h'` only, `backspace` will do same thing as `ctrl+h`, just like below:

```
registry.add_binding('c-h', filter=(HasFocus(DEFAULT_BUFFER) & ViInsertMode()))(nc.backward_char)
```

And `'c-?'` is not allowed to `add_binding`.

Is there a way to make it as many terminal can distinguish `c-h` and ``.

If for compatibility, is it possible to support bind `c-?`?

Thanks in advance.

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