Migrate events handling to reactivity in 'medea-jason' crate (#27, #47)

[evdokimovs]

Part of #27, #47

Synopsis

We need to handle server Event in medea-jason reactively and based on State. Thus, we will be able to synchronize client with server on reconnect by merging server's state with a client's one.

Solution

Create states for the all objects which are can be updated by the server's Event. Rewrite all Event handlers to update reactive State instead of real objects.

Checklist

• Created PR:
  • [x] In draft mode
  • [x] Name contains Draft: prefix
  • [x] Name contains issue reference
  • [x] Has k:: labels applied
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• [x] Documentation is updated (if required)
• [x] Tests are updated (if required)
• [x] Changes conform code style
• [x] CHANGELOG entry is added (if required)
• [x] FCM (final commit message) is posted
  • [x] and approved
• [x] Review is completed and changes are approved
• Before merge:
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  • [x] Draft: prefix is removed
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[evdokimovs]

FCM

Migrate events handling to reactivity in 'medea-jason' crate (#164, #27, #47)

- add Component and State for Sender, Receiver, Peer and PeerRepository
- rewrite EventHandler implementation to update Component's States instead of real objects

Additionally:
- upgrade Firefox to 84.0.2 version for E2E tests
- fix 'opt-level' being ignored when compiling 'medea-jason' crate in Cargo manifest
- globally set 'codegen-units = 1' in Cargo manifest