feat: toggle refinement styling

[thomasbritton]

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 7114974:

Sandbox	Source
example-instantsearch-getting-started	Configuration
example-react-instantsearch-getting-started	Configuration
example-react-instantsearch-next-app-dir-example	Configuration
example-react-instantsearch-next-routing-example	Configuration
example-vue-instantsearch-getting-started	Configuration

[sarahdayan]

I'm not sure why we need such selector, why not target .ais-ToggleRefinement-checkbox?

[thomasbritton]

This is because there is a selector in common.css that is of higher specificity input[class^='ais-'][type='checkbox']:checked { /* ... */ }

I did it this way because we were out of time so just needed something quick that would work but the class above probably needs to be merged into the refinement-list.css

[thomasbritton]

@sarahdayan I have re-worked so it uses the default class name .ais-ToggleRefinement-checkbox