[native] Warn the user when deleting a chat that has contained chats

Summary:
Part of ENG-4319.

Before deletion, the user is warned about possible contained chats. For subchannel deletion, the modal looks like this:
iOS:

Andriod:

When deleting a whole community, message changes:
iOS:

Android:

When there are no contained chats, the confirmation modal does not pop up.

Depends on D8526.

Test Plan: Same as D8530 test plan.

Reviewers: bartek, tomek, inka, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8590