[lib] Introduce translateClientDBMediaInfosToMedia(...)

Summary:
Given ClientDBMessageInfo we want to reconstruct an array of Media.

We'll consume translateClientDBMediaInfosToMedia(...) in multimedia-message-spec:rawMessageInfoFromClientDB to "unpersist" MULTIMEDIA messages stored in the SQLite messageStore.

Test Plan: Will be tested implicitly by subsequent diffs. Also included a simple unit test (will add some more later)

Reviewers: tomek, marcin, abosh, rohan, ginsu

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5313