Inline chat UI overhaul (#215927)

* don't dimiss inline chat content widget when already having typed something

https://github.com/microsoft/vscode-copilot/issues/6067

* extract `TextOnlyMenuEntryActionViewItem` for reuse

* remove unused variables

* * show chat input below request/response pairs
* setting for text-only buttons
* more dynamic buttons
* always show the first request, don't repopulate input with last message
* keep progress bar hidden, rely on "Generating..."
* no more special background color

* add `minimal` renderer style for chat renderings

* tweak font-size for details when render mode is minimal

* stable scroll position for inline chat, don't push down the lines chat is editing but push the inline chat upwards

* more buttons more compact, tweak labels

* * add missing service dependency
* repopulate input for some unit test

* allow output from `InteractiveChatController` suite