feat: Chat API and design refinements (#10577)
* feat: Chat API and design refinements
* fix padding when promptfield is size small
* update docs
* fix lint
* wrap user message in thread item if in thread
* fix lint
* alphabet is hard
* chat style consolidation
* fix lint
* Revert "wrap user message in thread item if in thread"
This reverts commit 6c1ccccf59742c828f3265a20a43d4e7d26df671.
* cleanup
* address review
* remove unneeded ThreadScrollButton export and usage
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Co-authored-by: Yihui Liao <44729383+yihuiliao@users.noreply.github.com>
Co-authored-by: Daniel Lu <dl1644@gmail.com>
