Migrate encryption state on room upgrade

[anoadragon453]

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file
• Pull request includes a sign off

Sytest PR: matrix-org/sytest#542

[codecov-io]

Codecov Report

Merging #4411 into develop will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           develop   #4411      +/-   ##
==========================================
+ Coverage    73.69%   73.7%   +0.01%     
==========================================
  Files          300     300              
  Lines        29819   29820       +1     
  Branches      4898    4898              
==========================================
+ Hits         21975   21979       +4     
+ Misses        6405    6401       -4     
- Partials      1439    1440       +1

Impacted Files	Coverage Δ
synapse/handlers/room.py	83.61% <ø> (ø)	⬆️
synapse/api/constants.py	100% <100%> (ø)	⬆️
synapse/handlers/search.py	80.24% <0%> (ø)	⬆️
synapse/handlers/federation.py	61.72% <0%> (ø)	⬆️
synapse/federation/federation_server.py	71.62% <0%> (+0.82%)	⬆️

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[richvdh]

well, that was complicated.

[ara4n]

clone_exiting_room or existing room ooi?

[ara4n]

why wouldn’t we clone all state? we don’t want widgets etc to vanish

[richvdh]

clone_exiting_room or existing room ooi?

oops

[richvdh]

why wouldn’t we clone all state? we don’t want widgets etc to vanish

well, for one, we can't clone the members, or the create...

It's not obvious to me that we want to copy any arbitrary state that a client may have set. Maybe, though.

[anoadragon453]

clone_exiting_room or existing room ooi?

oops

This is fixed in aaacb6c btw