[native] Blocking navigation in edit mode in ChatRouter

Summary: We prevent user from i.g. changing thread when we are in edit mode.

Test Plan:
Run the app on iOS and Android:

• checked if we can't navigate when we are in edit mode,
• checked if we can navigate after leaving exit mode.

Reviewers: michal, inka, ashoat, tomek

Reviewed By: ashoat, tomek

Subscribers: atul

Differential Revision: https://phab.comm.dev/D7630