New session icon

[mrleemurray]

We need a new icon to represent a new session - clicking on the icon would open a new chat session with the agent.

From the team:

We've got the Copilot and chat comment icons, and we essentially just need a variant of the “edit code” codicon that removes the “<>” and vertically centers the pencil (to represent a “new session” icon or equivalent)

Competitor icon:

Current edit-code icon:

@davidhosejr

[hawkticehurst]

Following up from Teams chat. The current icon (added in #439) looks just a touch large in relation to the icons it sits next to in the UI (screenshot 1).

Can we:

1. Reduce it's size a bit?
2. Could we also explore creating a outline (non-filled) version of the pencil a la what ChatGPT (screenshot 2) or Lucide does?