Fixes #56226

What?

Expose onBlur prop in ComboboxControl component to allow handling blur events.

Why?

Fixes #56226 where users need to reset pagination and search state when ComboboxControl loses focus, especially for AJAX-loaded data.

How?

1. Added onBlur prop to ComboboxControlProps interface
2. Modified onBlur handler to call parent's onBlur callback
3. Maintained existing blur functionality

Testing Instructions

<ComboboxControl
  onBlur={() => setPage(1)}
  // other props
/>

Screenshots or screencast

N/A - Functionality change only