Trigger Re-Render when Scrollability Changes and PermanentTrack is Enabled

[davidgolden]

Description

There is an edge case that exists where if permanentTrackY/X is enabled and the scrollability of the child content changes, a re-render is not triggered and therefore the component remains in its previous scrollable state. This happens because the primary place where a re-render is triggered in the update method is from updating the state only when scrollbar visibility has changed. This obviously never happens when permanentTrackX/Y is enabled. This PR adds a check for if the scrollability has changed and forced a re-render if it has.

Use case

This addresses issue #171 and can be replicated in https://codesandbox.io/s/sharp-engelbart-fnc2e?file=/src/App.js. It is applicable in situations when the scrollability of the underlying content changes, such as with dynamic content.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• [X ] Perform a code self-review
• [X ] Comment the code, particularly in hard-to-understand areas
• Update/add the documentation - since this is a bugfix I don't think this is necessary
• Write tests
• Ensure the test suite passes (yarn test) - tests were already not passing. this did not cause any additional tests to fail.
• Provide 100% tests coverage - see above