[lib] Introduce translateMediaToClientDBMediaInfos

Summary:
We previously had translateMediaToClientDBMediaInfo which gave us one ClientDBMediaInfo for each Media... but now the relationship between Media and "upload" is no longer 1:1.

translateMediaToClientDBMediaInfos replaces the existing function and returns an array with all of the ClientDBMediaInfos for a media message. By using this function in translateRawMessageInfoToClientDBMessageInfo we ensure that both the video and thumbnail are persisted in the media table of the SQLite "clientDB" database.

Test Plan:
Ensured that both video and thumbnail are stored in SQLite media table for video messages:

Also set breakpoints throughout to make sure values at different points were as expected.

Reviewers: tomek, marcin, abosh, rohan, ginsu

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5298