Make KeyboardManager public

[arguiot]

Hello, would it be possible to make the KeyboardManager public? Many people are complaining in the issues with bottom space and how to handle it: #1779. I had this issue personally, and the only way I fixed it was by accessing the keyboardManager object and rebind the inputAccessory like this:

keyboardManager.bind(inputAccessoryView: inputContainerView) { -50 }
keyboardManager.shouldApplyAdditionBottomSpaceToInteractiveDismissal = true

The problem is that to achieve this, you necessarily need to import MessageKit this way:

@testable import MessageKit

Which is not super nice...