Convert isUnread logic to unreadActionCount. Improve LHN unread chat stability.

[marcaaron]

Migrating some changes over from #525 which went off the rails

Wanted to take a step back and focus on improving the stability of the unread indicators in the LHN before adding any UI that will display their specific counts. Will be attempting to fix one or two bugs in the process.

Fixed Issues

Fixes https://github.com/Expensify/Expensify/issues/142988
Possibly Related to https://github.com/Expensify/Expensify/issues/142727

Tests

Test that leaving comments on a report works as expected

1. Leave a comment on a report
2. Verify that it shows normally
3. Leave another comment
4. Verify it looks fine
5. Refresh
6. Verify the comments persist

Test that a chat will show in the LHN if a new comment has been left on it while RNC is not running at all

1. Read all unread chats in the LHN
2. Completely close your e.cash session
3. Send several messages from another account
4. Open your e.cash session again
5. Verify the chat shows as unread

Test that a chat will show in the LHN if a new comment has been left on it and RNC is running

1. Read all unread chats in the LHN
2. Send one message from another account
3. Verify the chat shows as unread
4. Send another message from the same account as before
5. Verify the chat shows as unread still
6. Read the chat and click on another chat
7. Verify the chat disappears from the list

Test that reconnection callbacks will reveal a chat in LHN on reconnect

1. Read all unread chats in the LHN
2. Comment out the Pusher.init() line in HomePage
3. Go offline via the Network tab in Chrome Dev Tools
4. Add several comments to a chat report as another user
5. Go back online
6. Verify the reconnection callbacks fire and the LHN updates with the chat

Screenshots

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[marcaaron]

Ok this one is ready for another review.

[tgolen]

LGTM! We're gonna have conflicts :D Let's see who gets their's merged first.