ffi: add high level method for resetting the user's identity and deleting all associated secrets

[stefanceriu]

This PR adds support for completely resetting the user's identity and all their secrets. It will go through the following steps:

1. Disable backing up room keys and delete the active backup
2. Disable recovery (We can't delete account data events)
3. Remove previously known secrets by creating a new store (?)
4. Go through the cross-signing key reset flow
5. Finally, re-enable key backups only if they were enabled before

• Expose through FFI
• See if creating a new secrets store is necessary Not needed
• Check coverage to see if we need an OIDC specific test as well or whether the existing cross-singing tests suffice Looks good

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 84.09%. Comparing base (6fca1e8) to head (8895e53).
Report is 8 commits behind head on main.

Files	Patch %	Lines
crates/matrix-sdk/src/encryption/recovery/mod.rs	83.33%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3759      +/-   ##
==========================================
+ Coverage   84.07%   84.09%   +0.01%     
==========================================
  Files         259      259              
  Lines       27080    27098      +18     
==========================================
+ Hits        22767    22787      +20     
+ Misses       4313     4311       -2     

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[poljar]

Alright, this looks good. Feel free to get rid of the fixup commits and merge.