feat(css): Use gl-shadow-lg for drawer drop shadow

mentioned in commit a3ecc272

mentioned in merge request status-page!808 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!152 (merged)

mentioned in merge request gitlab!122120 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3424 (merged)

mentioned in merge request gitlab-docs!3959 (merged)