[lib] Rename `filterByNewThreadInfos` to `reassignMessagesToRealizedAndWatchedThreads`
[lib] Rename `filterByNewThreadInfos` to `reassignMessagesToRealizedAndWatchedThreads`

Summary: I think the new name better explains the behavior of the function. I'm very open to changing it to something more clear.

Test Plan: just a rename

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: palys-swm, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D1930

Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal