[native] Add some awaits in ChatInputBar.onSend

Summary:
I could add voids here instead, but I figured it doesn't particularly matter, since this function (onSend) is passed to TouchableOpacity's onPress prop, which doesn't care whether a Promise is returned, or how long the Promise takes.

Depends on D10168

Test Plan: Flow

Reviewers: michal, tomek

Reviewed By: michal

Differential Revision: https://phab.comm.dev/D10169