Crypto V2 fixes

[Anderas]

A number of changes / fixes for Crypto V2:

• re-decrypt events by specific sessionId after importing keys
• ensure we send room keys to our other devices
• better location for mac-specific crypto store (useful in integration tests)
• enable isUntrusted state for events
• fix a few nullability crashes

[codecov]

Codecov Report

Base: 36.22% // Head: 25.40% // Decreases project coverage by -10.81% ⚠️

Coverage data is based on head (ceae266) compared to base (d70c5af).
Patch coverage: 5.17% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #1630       +/-   ##
============================================
- Coverage    36.22%   25.40%   -10.82%     
============================================
  Files          582      582               
  Lines        92316    92348       +32     
  Branches     40130    40050       -80     
============================================
- Hits         33444    23465     -9979     
- Misses       57872    68107    +10235     
+ Partials      1000      776      -224     

Impacted Files	Coverage Δ
...o/Algorithms/RoomEvent/MXRoomEventDecryption.swift	0.00% <0.00%> (-68.84%)	⬇️
...trixSDK/Crypto/CrossSigning/MXCrossSigningV2.swift	0.00% <0.00%> (-21.25%)	⬇️
...trixSDK/Crypto/CryptoMachine/MXCryptoMachine.swift	0.00% <0.00%> (ø)
...chine/MXEventDecryptionResult+DecryptedEvent.swift	0.00% <0.00%> (-88.24%)	⬇️
...pto/KeyBackup/Engine/MXCryptoKeyBackupEngine.swift	0.00% <0.00%> (-48.91%)	⬇️
MatrixSDK/Crypto/MXCryptoV2.swift	0.81% <0.00%> (+<0.01%)	⬆️
...ms/RoomEvents/MXRoomEventDecryptionUnitTests.swift	0.00% <0.00%> (-98.64%)	⬇️
...s/Crypto/CryptoMachine/MXCryptoProtocolStubs.swift	0.00% <0.00%> (-51.32%)	⬇️
...sts/Crypto/Data/MXMegolmSessionDataUnitTests.swift	0.00% <0.00%> (-95.39%)	⬇️
...ckup/Engine/MXCryptoKeyBackupEngineUnitTests.swift	0.00% <0.00%> (-89.84%)	⬇️
... and 206 more

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[stefanceriu]

lgtm 👍