feat(DesignTokens): Replace illustration stroke width with unitless

mentioned in commit e427ecc0

mentioned in merge request status-page!903

mentioned in merge request gitlab!185188 (closed)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1600 (merged)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1601 (closed)

mentioned in merge request gitlab!185290 (closed)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4352 (merged)

mentioned in merge request gitlab!185824 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!67 (closed)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!367 (merged)