Replace the MessageInputBar with our new MessageInputBar library #730

We have decided to separate the MessageInputBar out into its own library. @nathantannar4 will be the lead maintainer on that project. This allows us to provide other optional subspecs to MessageKit project such as autocomplete and attachment managers without bloating the original project.

This will be available in MessageKit 2.0 as it is a heavy new feature with API breaking changes.

cc @nathantannar4 can you submit a PR against the MessageKit development branch making this addition?