Missing features from multi-chat tabs

This tabs should feel vscode native and have the same basic interactions as other tabs in vscode. Ideally we would reuse components and not reimplement them. The main things I'm missing right now are middle-click to close, and dnd to reorder.

At one point, messing with it, I got into a state where the chat view was showing a chat that was not actually open in a tab, but I can't repro it