feat(GlCollapsibleListbox): improve a11y support

mentioned in commit dbe4c3f0

mentioned in merge request gitlab-svgs!1164 (merged)

mentioned in merge request gitlab-org/technical-writing/docs-gitlab-com!683 (merged)

mentioned in merge request gitlab!191093 (merged)

mentioned in merge request gitlab-svgs!1167 (closed)

mentioned in merge request status-page!903

mentioned in merge request gitlab!191470 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4433 (merged)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1731 (merged)