Tracks being able to flutter run for macOS, Windows, and Linux.

This will likely be implemented in phases, first being able to flutter run using a prebuilt application on each platform (already implemented behind flags for macOS), then later once #30706 is done having the full behavior of building and then running.

Any support we can provide for this in the short term is very valuable for the workflow of people trying out early stages of the desktop support, since being able to flutter run provides compatibility with existing Flutter support in tools and IDEs (e.g., hot reload, and source-level debugging).