Simplify arg creation in component stories

In our component stories, we often use inline defaultValue and generateProps helpers to build the args for the component. For reasons described in gitlab-org/gitlab-ui!3278 (merged), this isn't strictly necessary, and can even cause bugs.

This issue is about simplifying all stories in a manner similar to gitlab-org/gitlab-ui!3278 (merged). This either means a few MRs connected to this issue, or to promote this to an epic and create issues for each story. The former is probably good enough.