Change Testing to use Cypress Component Testing

[mattfwood]

Currently we're using Jest to run our tests, but for something like a component library it would be much more powerful / useful / accurate to use something like Cypress Component Testing.

This will likely be a big rework but it can be done gradually by component.

It would also enable us to use powerful features like Cypress snapshots, which could enable visual image diffing for components to make sure we don't accidentally change the appearance of components.