Slot/Fill: Error when provider is missing

[sirreal]

The design of Slot/Fill context hides problematic cases where a Consumer is not mounted under the necessary Provider.

It would be preferable to remove the stubbed context that hides misuse in applications. I'd like to see a descriptive error thrown immediately when the context is used without a provider:

gutenberg/packages/components/src/slot-fill/bubbles-virtually/slot-fill-context.js

Lines 1 to 16 in 6773860

	/**
	* WordPress dependencies
	*/
	import { createContext } from '@wordpress/element';
	const SlotFillContext = createContext( {
	slots: {},
	fills: {},
	registerSlot: () => {},
	updateSlot: () => {},
	unregisterSlot: () => {},
	registerFill: () => {},
	unregisterFill: () => {},
	} );
	export default SlotFillContext;

An error in useSlot seems ideal:

gutenberg/packages/components/src/slot-fill/bubbles-virtually/use-slot.js

Line 12 in 6773860

const registry = useContext( SlotFillContext );

const SlotFillContext = createContext( undefined );
function useSlot( name ) {
  const registry = useContext( SlotFillContext );
  if ( ! registry ) {
    throw new Error( 'useSlot must be a descendent of SlotFillProvider' );
  }
  // …
}

#23014 describes a bug where SlotFillProvider is not an ancestor of a SlotFillContext Consumer.

#23108 fixes the error, but the caveats were noted in several places.

cc: @gziolo @youknowriad @diegohaz