ComboboxControl needs placeholder text or Ref hook

[vilu85]

What problem does this address?

ComboboxControl does not have a placeholder text and cannot be added by referring to a DOM element because the Ref-hook is also missing.

What is your proposed solution?

By adding placeholder prop or exposing inputContainer

gutenberg/packages/components/src/combobox-control/index.js

Line 67 in 604561d

const inputContainer = useRef();

ref through props.