What?

Updates the CustomGradientBar component to satisfy the exhaustive-deps eslint rule (specifically by updating the ControlPoints subcomponent)

Why?

Part of the effort in #41166 to apply exhuastive-deps to the Components package

How?

GradientPickerDropdown
Update the popoverProps useMemo dependency array to include gradientPickerDomRef instead of gradientPickerDomRef.current.

useEffect to clean event listeners on unmount
The dependency array is currently empty, which works to trigger the cleanup only on unmount. Unfortunatelyexhaustive-deps expects to see the function being called in the dependency array, which would cause it to trigger on every render.

To avoid that, if we wrap cleanEventListeners in its own useCallback the listeners aren't able to be cleaned properly. Using a ref of the function instead allows us to exclude it from the dependency array so our useEffect can provide the intended cleanup, without disrupting the actual user interactions with the component.

Took me a little bit to arrive at this solution, and I'm very open to feedback if there are other/better approaches :)

Testing Instructions

1. From your local Gutenberg directory, run npx eslint --rule 'react-hooks/exhaustive-deps: warn' packages/components/src/custom-gradient-bar
2. Confirm that the linter returns no errors
3. Confirm e2e tests still pass