[native] Add EditState to the InputState

Summary: Added EditState which stores information about which message is being currently edited.

Test Plan: Run the app, and check if it still works. More tests are in later diffs.

Reviewers: michal, inka, ginsu

Reviewed By: inka

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7342