Problem:
`msg_show` has "progress" info (title, status, percent) which is not presented
by default.
Solution:
Format TUI messages as `{title}: {msg}...{percent}%`. This also gets sent to UI.
- With specific formatting sent to UI we can remove the `progress` item from
`msg_show` event. It can be added if needed in the future. Also, having
a default presentation makes the feature more useful.
- For `vim._extui` we just need to implement the replace-msg-with-same-id
behavior.
- If any UI/plugin wants to do anything fancier, they can handle the `Progress`
event.
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