feat(GlFormSelect): Add class property

mentioned in commit 5e52d847

mentioned in merge request status-page!903

mentioned in merge request gitlab!170894 (closed)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1211 (closed)

mentioned in merge request gitlab!170923 (merged)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1212 (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/editor-extensions/gitlab-jetbrains-plugin!1249 (closed)

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