R1:e5580d038dd1

Improve Conpherence column textarea JS behaviors

Summary:
- Don't show a loading state on the whole column while sending chat. We could show some kind of minor loading state, but standard JX.Busy stuff will kick in after a couple seconds anyway.
- Blank the textarea immediately on submit so you can start typing more text.
- Don't disable the form while submiting; disabling it prevents you from typing more text.
- Hide the placeholder while the textarea is focused. If we don't do this, the…