Before this diff, useSidebarInfos would return lastUpdatedAtLeastTime as lastUpdatedTime, as a temporary hack to help split up my work into smaller diffs.

In an earlier diff we updated lastUpdatedTime to be a Promise, and this allows us to avoid refactoring everything to handle the Promise.

In this diff, we address this temporary hack for sidebars, but for not for the ChatThreadItem itself (which will be handled later).

useSidebarInfos is used in places outside of chat-selectors.js, so this required some additional refactoring.

Depends on D13914

Tested in combination with the rest of the stack. See video in D13918