[lib] Displaying edited content in a pending thread

Summary: When the user wants to create a thread from an edited message, we want him to see the updated content of the message.

Test Plan:

• [web & iOS] edited a message, clicked on it to create a sidebar from it, I can see updated content,
• [web] on the pending thread route refreshed site, checked how it behaves: it just redirects to the main thread.

Reviewers: michal, inka, ginsu, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7140