[Enhancement]: Form component input props should allow passing of custom callbacks

[joshuatf]

Describe the solution you'd like

For the Form component getInputProps, we occasionally have to override an event like onBlur.

<TextControl
  { ...getInputProps( 'field_name' ) }
  onBlur={ myOnBlurHandler }
/>

The problem is that this overrides the default getInputProps onBlur method and now manually needs to be called:

<TextControl
  { ...getInputProps( 'field_name' ) }
  onBlur={ () => {
    myOnBlurHandler();
    getInputProps( 'field_name' ).onBlur();
  }
/>

To make things a bit easier on consumers, we could consider an optional second argument that adds props to the event without overriding the Form's handlers. E.g.,

<TextControl
  { ...getInputProps( 'field_name', { onBlur: myOnBlurHandler } ) }
/>

Describe alternatives you've considered

Manually calling the input form's handler is the current way of handling this, but it is more prone to errors and more cumbersome to write.

getInputProps( 'field_name' ).onBlur();

Additional context

The new product management experience has been creating utils like getTextControlProps and getInputControlProps that handle specific items like classes. It would be good to move some of this logic back to the Form package.