Why this change?
Previously, we were preloading the necessary metadata for
`adminCustomizeThemes.show.schema` route in the
`adminCustomizeThemes.show` route. This is wasteful because we're
loading data upfront when the objects setting editor may not be used.
This change also lays the ground work for a future commit where we need
to be shipping down additional metadata which may further add to the
payload.
Alan Guo Xiang Tan