feat(toggle): use design tokens for is-disabled colors and clean up styling

mentioned in commit 9defa96b

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1132 (merged)

mentioned in merge request status-page!903

mentioned in merge request gitlab!168779 (merged)

mentioned in merge request gitlab!168825 (closed)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1147 (closed)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!55 (closed)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!352 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!58 (merged)