When Copilot Code Review (CCR) no-ops, there's no notice to user as to why

[jruales]

Type: Bug

1. Invoke Copilot Code Review (Right click -> Generate Code -> Review) without any selection (no manual nor automatic selection), so that it no-ops without adding any comments. For example:
   1. Open or create a Markdown file with some text but no headers (no #, ##, ###, etc.)
   2. Without selecting any text, Right click -> Generate Code -> Review
2. 🐛 Nothing happens, and the user has no idea why

Expected:

• Option 1: Assume the selection is the entire file (or maybe current line) if there's no selection, to guarantee some comment to happen. This prevents the no-op in the first place
• Option 2: If we want to preserve the existing behavior with the no-op, at least inform the user why nothing happens. For example, let them know that a selection is necessary

in this Issue comment (#275624 (comment)) is an example video of the confusion that can cause if the user sees no notice nor any comment

• Copilot Chat Extension Version: 0.33.2025110703
• VS Code Version: Version: 1.106.0-insider (Universal)
• OS Version:
• Feature (e.g. agent/edit/ask mode): Copilot Code Review
• Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet): N/A
• Logs: N/A