[functions] Firebase CLI integration

[dackers86]

Implement full Firebase CLI integration for Dart functions. This includes:

• Support for deployment of Dart functions
• Support for local emulation of Dart functions
• Utilizing the file-based discovery mechanism (detectFromYaml) to read the generated spec from .dart_tool directory
• Spawning two processes:
  1. build_runner process for spec file generation and watching
  2. User's Dart entrypoint file execution with HTTP server

Local Development:
To test locally, use npm link in the firebase-tools repository:

1. Clone firebase-tools repository
2. Run npm install in firebase-tools
3. Run npm link to create global symlink
4. In your test project, run npm link firebase-tools

Dependencies:

• [functions] Dart runtime delegate
• [functions] Emulator integration and reloading

Acceptance Criteria:

• Deployment of Dart functions working
• Local emulation working
• File-based discovery (detectFromYaml) implemented
• Dual process spawning working
• Local development instructions documented