feat(GlBroadcast): Create and use design tokens

mentioned in commit 1c5b7d38

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!929 (merged)

mentioned in merge request status-page!903

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4039 (merged)

mentioned in merge request gitlab!165456 (closed)

mentioned in merge request gitlab!165458 (merged)

mentioned in commit 89c8ab43

mentioned in merge request gitlab!165726 (merged)

mentioned in merge request gitlab!166177 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!348 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!50 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!349 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!51 (merged)