PERF: Do not include thumbnail information in default topic list payload (PR #10163)

Now it is only included when a theme/plugin has requested it.


In include_excerpt? we’re already creating an instance of ThemeModifierHelper, perhaps we can memoize the instance of ThemeModifierHelper and reuse that here?

We could, but ThemeModifierHelper is extremely lightweight, so I don’t think it should make much difference?

Ooops sorry just saw that include_excerpt? doesn’t always create the instance of ThemeModifierHelper.