🐛 Bug(chat-input-textarea): Textarea display should follow cursor, plus should disable enter to submit on mobile

[KemingHe]

Expected Behaviors/User Sub-Stories

• On both, instead of expand/retract with button, textarea does it automatically up to a certain limit, and past such limit will trigger overflow-y-auto, mimicking GitHub Copilot user story.
• On both, when adding a newline, the newline should be from where existing cursor is, NOT always default to end of text.
• On both, when adding a newline, the text should auto-scrolls to cursor location.
• On mobile, pressing enter adds a newline.
• On desktop, pressing enter submits the form (containing message).
• On desktop, pressing shift+enter adds a newline.

Observed Behavior (Wrong)

• On both, textarea can only have two heights, dictated by a expand button with state management (cumbersome).
• On both, when adding a newline, the newline always goes to end of text, not where the actual cursor is.
• On both, the text doesn't auto-scroll when a new line is added.
• On mobile, presssing enter submits the form.