[native] Introduce migration to unshim MULTIMEDIA messages

Summary:
Context: https://linear.app/comm/issue/ENG-2270/handle-unshimming-of-multimedia-messages-on-native

This migration handles "unshimming" UNSUPPORTED messages that wrap MULTIMEDIA messages for clients upgrading from an old client to one that supports video messages.

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Depends on D5637

Test Plan:
Set breakpoints and ensured that values were as expected at each point.

1. Sent video message to native client that didn't support video messages and observed UNSUPPORTED message in Redux that wrapped MULTIMEDIA message.

2. Bumped Redux persist version to trigger migration.

3. Observed that UNSUPPORTED message was replaced by "unshimmed` MULTIMEDIA message.

I'll do a lot more additional testing before landing.

Reviewers: tomek, marcin, ginsu, rohan, kamil, ashoat

Reviewed By: ashoat

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D5638