compose: Support editing an already-sent message

[lakshya1goel]

Fixes: #126

Video Recording

WhatsApp.Video.2025-02-03.at.2.26.56.PM.mp4

Screenshots

Step 1	Step 2	Step 3

Success	Failure

[gnprice]

Thanks @lakshya1goel for picking this up!

This will be an exciting feature but also a complex one, which is a major reason why it's in the M6 Post-launch milestone rather than M5 Launch or earlier. Yesterday after looking back at the last few weeks' progress, I determined we should start focusing more strictly on the M5a and M5 Launch milestones in order to get the app launched to everyone on schedule. Given that, let's put this PR on hold for now until the launch is ready.

[gnprice]

Closing this because this is a complex issue, and I think this PR doesn't yet have a lot in common with a direction that I'd want to see for an implementation of this that we merge. More context here: #126 (comment)

@lakshya1goel thanks for trying this out; I'd encourage first revising your reviewed PRs, and then taking a look at our other launch issues. On the board I see at least one "help wanted" launch issue still unclaimed.