SuperEditor is used by some clients to compose rich text messages that are sent to chat. Sometimes human chat, sometimes AI chat. After sending the message, it needs to be displayed in a conversation. Clients can display those messages with SuperReader, but SuperReader requires special widgets to support intrinsic height, and currently doesn't support intrinsic width at all.

The reality is, SuperReader's internal scrolling system is irrelevant for chat use-cases, but in chat, the whole conversation is scrollable, with each message taking up however much space it wants. We should better support this use-case.

Create a SuperChatBubble widget, which is the same as SuperReader, except it doesn't include any of its own scrolling dynamics. It builds all components into a column, and is sized intrinsically for its width and height.