New Compiler Feature Setup

Set up tracking for a new C# language feature in dotnet/roslyn, starting from an implementation PR.

IMPORTANT: Present the full plan and get explicit user confirmation before making any changes.

IDEMPOTENCY: Safe to re-run. Checks for existing artifacts before creating. Use it to fix missing pieces.

Prerequisites

• gh CLI authenticated with write access to dotnet/roslyn (verify with gh auth status)

Do not proceed if prerequisites are not met. Instead, guide the user through the necessary actions (installing gh, authenticating, etc.).

Phase 1: Gather

1.1 Parse the PR