Modifying types and callsites to reflect new olm API.

Depends on D12203

Tested end-to-end:

1. Tested content session with OTKs on both web and native
2. Tested content session without OTKs on both web native
3. Tested notifs
4. Tested backward compatibility: @marcin was running his devices logged to staging on old olm version, and I was running the new version (this stack). WIth one OTKs it works as previously (tested both me and Marcin sending requests to each other and tested both platform). When there are no OTKs Marcin was unable to create a session request (same as now), I was able to create a session request, but it failed on Martin’s device with BAD_MESSAGE_KEY_ID but without crashing the app.