[lib] Make useInlineSidebarText hook parameter optional

Summary:
When we add reactions to InlineSidebar component we want to support the case, when there are reactions and there is no existing thread from the message.
In that case, we don't have ThreadInfo. The idea is to make the hook return empty strings when no there is threadInfo provided. It will help avoid conditional execution of the hook in that case.

Test Plan: Current behavior remain unchaged. After introducing InlineSidebar redesign, confirmed that the hook returns empty result strings when there is no thread provided.

Reviewers: tomek, atul, abosh

Reviewed By: tomek, abosh

Subscribers: ashoat, adrian

Differential Revision: https://phab.comm.dev/D4823