Interactive QTextObjectInterfaces

For many usecases, such as mentions in a chat application, it is desirable to add non-text elements inside the flow of text. The current QTextObjectInterface APIs work fine for this, but fail to provide APIs for interactive elements.

Namely, the following APIs are lacking for the interactive elements usecase:

• an API to let the QTextDocument know the QTextObjectInterface wants to redraw itself for whatever reason; e.g. an animation
• event APIs to the QTextObjectInterface, e.g. hover, click/tap, focus, etc.